Scripting Languages: PHP, Perl, Python, Ruby

a side-by-side reference sheet

arithmetic and logic | strings | dates and time | arrays | dictionaries | functions | execution control | environment and i/o | libraries and modules | objects | reflection | web | java interop | history | contact | edit

php (1995) perl (1987) python (1991) ruby (1995)
versions used
 
5.3 5.10; 5.12; 5.14 2.6; 2.7; 3.2 1.8; 1.9
show version
 
$ php --version $ perl --version $ python -V $ ruby --version
interpreter
 
$ php -f foo.php $ perl foo.pl $ python foo.py $ ruby foo.rb
repl
 
$ php -a $ perl -de 0 $ python $ irb
statement separator
 
; ; ; # or sometimes newline ; # or sometimes newline
block delimiters
 
{} {} offside rule {}
do end
assignment
 
$v = 1; $v = 1; # does not return a value:
v = 1
v = 1
parallel assignment
 
list($x, $y, $z) = array(1 ,2, 3);
# 3 is ignored:
list($x, $y) = array(1, 2, 3);
# $z set to NULL:
list($x, $y, $z) = array(1, 2);
($x, $y, $z) = (1, 2, 3);
# 3 is ignored:
($x, $y) = (1, 2, 3);
# $z set to undef:
($x, $y, $z) = (1, 2);
x, y, z = 1, 2, 3
# raises ValueError:
x, y = 1, 2, 3
# raises ValueError:
x, y, z = 1, 2
x, y, z = 1, 2, 3
# 3 is ignored:
x, y = 1, 2, 3
# z set to nil:
x, y, z = 1, 2
swap
 
list($x, $y) = array($y, $x); ($x, $y) = ($y, $x); x, y = y, x x, y = y, x
compound assignment operators: arithmetic, string, logical, bit += -= *= none /= %= **=
.= none
&= |= none
<<= >>= &= |= ^=
+= -= *= none /= %= **=
.= x=
&&= ||= ^=
<<= >>= &= |= ^=
# do not return values:
+= -= *= /= //= %= **=
+= *=
&= |= ^=
<<= >>= &= |= ^=
+= -= *= /= none %= **=
+= *=
&&= ||= ^=
<<= >>= &= |= ^=
increment and decrement
 
$x = 1;
++$x;
--$x;
$x = 1;
++$x;
--$x;
none x = 1
# x not mutated:
x.succ
x.pred
local variable declarations
 
# in function body:
$v = NULL;
$a = array();
$d = array();
$x = 1;
list($y, $z) = array(2, 3);
my $v;
my (@a, %d);
my $x = 1;
my ($y, $z) = (2, 3);
# in function body:
v = None
a, d = [], {}
x = 1
y, z = 2, 3
v = nil
a, d = [], {}
x = 1
y, z = 2, 3
regions which define local scope top level:
  function or method body

nestable (with use clause):
  anonymous function body
top level:
  file

nestable:
  function body
  anonymous function body
  anonymous block
nestable (read only):
  function or method body
top level:
  file
  class block
  module block
  method body

nestable:
  anonymous function block
  anonymous block
global variable list($g1, $g2) = array(7, 8);
function swap_globals() {
  global $g1, $g2;
  list($g1, $g2) = array($g2, $g1);
}
our ($g1, $g2) = (7, 8);
sub swap_globals() {
  ($g1, $g2) = ($g2, $g1);
}
g1, g2 = 7, 8
def swap_globals():
  global g1, g2
  g1, g2 = g2, g1
$g1, $g2 = 7, 8
def swap_globals()
  $g1, $g2 = $g2, $g1
end
constant declaration
 
define("PI", 3.14); use constant PI => 3.14; # uppercase identifiers
# constant by convention

PI = 3.14
# warning if capitalized
# identifier is reassigned

PI = 3.14
to-end-of-line comment
 
// comment
# comment
# comment # comment # comment
comment out multiple lines
 
/* comment line
another line */
=for
comment line
another line
=cut
use triple quote string literal:
'''comment line
another line'''
=begin
comment line
another line
=end
null
 
NULL # case insensitive undef None nil
null test
 
is_null($v)
! isset($v)
! defined $v v == None
v is None
v == nil
v.nil?
undefined variable access
 
NULL error under use strict; otherwise undef raises NameError raises NameError
undefined test
 
same as null test; no distinction between undefined variables and variables set to NULL same as null test; no distinction between undefined variables and variables set to undef not_defined = False
try: v
except NameError: not_defined = True
! defined?(v)
arithmetic and logic
php perl python ruby
true and false
 
TRUE FALSE # case insensitve 1 '' True False true false
falsehoods
 
FALSE NULL 0 0.0 '' '0' array() undef 0 0.0 '' '0' () False None 0 0.0 '' [] {} false nil
logical operators
 
&& || ! lower precedence: and or xor && || ! lower precedence: and or xor not and or not and or not also: && || !
conditional expression
 
$x > 0 ? $x : -$x $x > 0 ? $x : -$x x if x > 0 else -x x > 0 ? x : -x
comparison operators
 
== != or <> > < >= <=
no conversion: === !==
numbers only: == != > < >= <=
strings: eq ne gt lt ge le
== != > < >= <= == != > < >= <=
convert from string, to string
 
7 + '12'
73.9 + '.037'
'value: ' . 8
7 + '12'
73.9 + '.037'
'value: ' . 8
7 + int('12')
73.9 + float('.037')
'value: ' + str(8)
7 + "12".to_i
73.9 + ".037".to_f
"value: " + "8".to_s
arithmetic operators
 
+ - * / none % pow(b,e) + - * / none % ** + - * / // % ** + - * x.fdiv(y) / % **
integer division
 
(int) (13 / 5)
none
int ( 13 / 5 )
none
13 // 5
q, r = divmod(13, 5)
13 / 5
q, r = 13.divmod(5)
float division
 
13 / 5 13 / 5 float(13) / 5
# python 3:
13 / 5
13.to_f / 5 or
13.fdiv(5)
arithmetic functions
 
sqrt exp log sin cos tan asin acos atan atan2 use Math::Trig qw(
  tan asin acos atan);

sqrt exp log sin cos tan asin acos atan atan2
from math import sqrt, exp, log, \
sin, cos, tan, asin, acos, atan, atan2
include Math
sqrt exp log sin cos tan asin acos atan atan2
arithmetic truncation
 
(int)$x
round($x)
ceil($x)
floor($x)
abs($x)
use POSIX qw(ceil floor);

int($x)
install Number::Format
ceil($x)
floor($x)
abs($x)
import math

int(x)
int(round(x))
math.ceil(x)
math.floor(x)
abs(x)
x.to_i
x.round
x.ceil
x.floor
x.abs
min and max
 
min(1,2,3)
max(1,2,3)
# of an array:
$a = array(1,2,3)
call_user_func_array(min, $a)
call_user_func_array(max, $a)
use List::Util qw(min max);

min(1,2,3);
max(1,2,3);
@a = (1,2,3);
min(@a);
max(@a);
min(1,2,3)
max(1,2,3)
min([1,2,3])
max([1,2,3])
[1,2,3].min
[1,2,3].max
division by zero
 
returns FALSE with warning error raises ZeroDivisionError integer division raises ZeroDivisionError
float division returns Infinity
integer overflow
 
converted to float converted to float; use Math::BigInt to create arbitrary length integers becomes arbitrary length integer of type long becomes arbitrary length integer of type Bignum
float overflow
 
INF inf raises OverflowError Infinity
sqrt -2
 
NaN error unless use Math::Complex in effect # raises ValueError:
import math
math.sqrt(-2)
# returns complex float:
import cmath
cmath.sqrt(-2)
raises Errno::EDOM
rational numbers
 
none use Math::BigRat;

my $x3 = Math::BigRat->new('22/7');
$x->numerator();
$x->denominator();
from fractions import Fraction

x = Fraction(22,7)
x.numerator
x.denominator
require 'rational'

x = Rational(22,7)
x.numerator
x.denominator
complex numbers
 
none use Math::Complex;

my $z = 1 + 1.414 * i;
Re($z);
Im($z);
z = 1 + 1.414j
z.real
z.imag
require 'complex'

z = 1 + 1.414.im
z.real
z.imag
random integer, uniform float, normal float rand(0,99)
lcg_value()
none
int(rand() * 100)
rand()
none
import random
 
random.randint(0,99)
random.random()
random.gauss(0,1)
rand(100)
rand
none
bit operators
 
<< >> & | ^ ~ << >> & | ^ ~ << >> & | ^ ~ << >> & | ^ ~
binary, octal, and hex literals none
052
0x2a
0b101010
052
0x2a
0b101010
052
0x2a
0b101010
052
0x2a
base conversion base_convert("42", 10, 7);
base_convert("60", 7, 10);
none
none
none
int("60", 7)
42.to_s(7)
"60".to_i(7)
strings
php perl python ruby
string literal
 
'don\'t say "no"'
"don't say \"no\""
'don\'t say "no"'
"don't say \"no\""
'don\'t say "no"'
"don't say \"no\""
'don\'t say "no"'
"don't say \"no\""
newline in literal
 
yes yes no, use escape or triple quote literal yes
backslash escapes
 
single quoted:
\' \\
double quoted:
\f \n \r \t \v \xhh \$ \" \ooo
single quoted:
\' \\
double quoted:
\a \b \cx \e \f \n \r \t \xhh \x{hhhh} \ooo
\newline \\ \' \" \a \b \f \n \r \t \v \ooo \xhh
python 3:
\uhhhh
single quoted:
\' \\
double quoted:
\a \b \cx \e \f \n \r \s \t \uhhhh \u{hhhhh} \v \xhh \ooo
variable interpolation
 
$count = 3;
$item = "ball";
echo "$count ${item}s\n";
my $count = 3;
my $item = "ball";
print "$count ${item}s\n";
none count = 3
item = "ball"
puts "#{count} #{item}s"
custom delimiters my $s1 = q[foo bar];
my $s2 = qq[$s1 baz];
s1 = %q[foo bar]
s2 = %Q[#{s1} baz]
sprintf
 
$fmt = "foo: %s %d %f";
sprintf($fmt, 'bar', 13, 3.7);
my $fmt = "foo: %s %d %f";
sprintf($fmt, 'bar', 13, 3.7)
'foo: %s %d %f' % ('bar',13,3.7)
 
fmt = 'foo: {0} {1} {2}'
str.format(fmt, 'bar', 13, 3.7)
"foo: %s %d %f" % ['bar',13,3.7]
here document
 
$computer = 'PC';
$s = <<<EOF
here document
there $computer
EOF
;
$computer = 'PC';
$s = <<EOF;
here document
there $computer

EOF
none computer = 'PC'
s = <<EOF
here document
there
#{computer}
EOF
concatenate
 
"hello, " . "world" "hello, " . "world" 'hello, ' + 'world' "hello, " + "world"
replicate
 
$hbar = str_repeat('-', 80); my $hbar = '-' x 80; hbar = '-' * 80 hbar = '-' * 80
split
 
explode(" ","foo bar baz")
preg_split('/\s+/',"foo bar baz")
split(/\s+/,"foo bar baz") 'foo bar baz'.split() "foo bar baz".split
join
 
$a = array("foo","bar","baz");
implode(" ", $a)
join(' ',("foo","bar","baz")) ' '.join(['foo','bar','baz']) ['foo','bar','baz'].join(' ')
case manipulation strtoupper("hello")
strtolower("HELLO")
ucfirst("hello")
uc("hello")
lc("HELLO")
ucfirst("hello")
'hello'.upper()
'HELLO'.lower()
'hello'.capitalize()
"hello".upcase
"HELLO".downcase
"hello".capitalize
strip
 
trim(" foo ")
ltrim(" foo")
rtrim("foo ")
use regex substitution ' foo '.strip()
' foo'.lstrip()
'foo '.rstrip()
" foo ".strip
" foo".lstrip
"foo ".rstrip
pad on right, on left
 
str_pad("hello", 10)
str_pad("hello", 10, " ",
        STR_PAD_LEFT)
sprintf("%-10s","hello")
sprintf("%10s","hello")
'hello'.ljust(10)
'hello'.rjust(10)
"hello".ljust(10)
"hello".rjust(10)
length
 
strlen("hello") length("hello") len('hello') "hello".length
"hello".size
index of substring
 
strpos("foo bar", "bar")
returns FALSE if not found
index("foo bar","bar")
returns -1 if not found
'foo bar'.index('bar')
raises ValueError if not found
"foo bar".index("bar")
returns nil if not found
extract substring
 
substr("foo bar", 4, 3) substr("foo bar",4,3) "foo bar"[4:7] "foo bar"[4,3]
extract character syntax error to use index notation directly on string literal:
$s = "foo bar";
$s[4];
can't use index notation with strings:
substr("foo bar",4,1)
"foo bar"[4] "foo bar"[4]
chr and ord
 
chr(65)
ord("A")
chr(65)
ord("A")
chr(65)
ord('A')
65.chr
"A".ord
character count
 
$a = count_chars("(3*(7+12))");
$a[ord('(')]
"(3*(7+12))" =~ tr/(// '(3*(7+12))'.count('(') '(3*(7+12))'.count('(')
character translation
 
$ins = implode(range('a','z'));
$outs = substr($ins,13,13) . substr($ins,0,13);
strtr("hello",$ins,$outs)
$s = "hello";
$s =~ tr/a-z/n-za-m/;
from string import lowercase as ins
from string import maketrans
outs = ins[13:] + ins[:13]
"hello".translate(maketrans(ins,outs))
"hello".tr('a-z','n-za-m')
regexp match
 
preg_match('/^\d{4}/',"1999")
preg_match('/^[a-z]+/',"foo BAR")
preg_match('/[A-Z]+/',"foo BAR")
"1999" =~ /^\d{4}$/
"foo BAR" =~ /^[a-z]+/
"foo BAR" =~ /[A-Z]+/
import re
re.match("\d{4}$","1999")
re.match("[a-z]+","foo BAR")
re.search("[A-Z]+","foo BAR")
"1999".match(/^\d{4}$/)
"foo BAR".match(/^[a-z]+/)
"foo BAR".match(/[A-Z]+/)
match, prematch, postmatch
 
none my $s = "A 17 B 12";
while ( $s =~ /\d+/ ) {
  my $discard = $`;
  my $number = $&;
  $s = $';
  print $number . "\n";
}
s = "A 17 B 12"
while True:
  m = re.search('\d+',s)
  if not m:
    break
  discard = s[0:m.start(0)]
  number = m.group()
  s = s[m.end(0):len(s)]
  print(s)
s = "A 17 B 12"
while (/\d+/.match(s)) do
  discard = $`
  number = $&
  s = $'
  puts number
end
substring matches
 
$a = array();
$s = "2010-06-03";
$r = '/(\d{4})-(\d{2})-(\d{2})/';
preg_match($r, $s, $a);
list($_, $yr, $mn, $dy) = $a;
"2010-06-03" =~ /(\d{4})-(\d{2})-(\d{2})/;
($yr, $mn, $dy) = ($1, $2, $3);
import re
reg = "(\d{4})-(\d{2})-(\d{2})"
m = re.search(reg, "2010-06-03")
yr,mn,dy = m.groups()
reg = /(\d{4})-(\d{2})-(\d{2})/
m = reg.match("2010-06-03")
yr,mn,dy = m[1..3]
scan
 
$s = "foo bar baz";
preg_match_all('/\w+/', $s, $a);
$a[0]
$s = "foo bar baz";
@a = $s =~ m/\w+/g;
import re
s = 'foo bar baz'
re.compile('\w+').findall(s)
"foo bar baz".scan(/\w+/)
single substitution
 
$s = 'foo bar bar';
preg_replace('/bar/','baz',$s,1);
$s = "foo bar bar";
$s =~ s/bar/baz/;
$s
import re
s = 'foo bar bar'
re.compile('bar').sub('baz', s, 1)
"foo bar bar".sub(/bar/,'baz')
global substitution
 
$s = 'foo bar bar';
preg_replace('/bar/', 'baz', $s);
$s = "foo bar bar";
$s =~ s/bar/baz/g;
$s
import re
s = 'foo bar bar'
re.compile('bar').sub('baz', s)
"foo bar bar".gsub(/bar/,'baz')
dates and time
php perl python ruby
date/time type
 
integer with Unix epoch or DateTime integer with Unix epoch or tm array datetime.datetime Time
current date/time contains Unix epoch; hence always UTC:
$t = time();
DateTime objects:
$dt = new DateTime("now");
$utc_dtz = new DateTimeZone("UTC");
$utc = new DateTime("now", $utc_dtz);
contains Unix epoch; hence always UTC:
$t = time;
tm arrays:
@tm = localtime($t);
@tm_utc = gmtime($t);
import datetime
 
t = datetime.datetime.now()
utc = datetime.datetime.utcnow()
t = Time.now
utc = Time.now.utc
local timezone DateTime objects can be instantiated without specifying the timezone if a default is set:
$tmz = "America/Los_Angeles";
date_default_timezone_set($tmz);
tm arrays do not contain the offset or timezone name a datetime object has no timezone information unless a tzinfo object is provided when it is created if no timezone is specified the local timezone is used
strftime strftime("%Y-%m-%d %H:%M:%S", $t);
date("Y-m-d H:i:s", $t);
$dt->format("Y-m-d H:i:s");
use POSIX qw(strftime);
 
@tm = localtime(time);
$fmt = "%Y-%m-%d %H:%M:%S";
print strftime($fmt, @tm);
t.strftime("%Y-%m-%d %H:%M:%S") t.strftime("%Y-%m-%d %H:%M:%S")
strptime $fmt = "Y-m-d H:i:s";
$s = "2011-05-03 10:00:00";
$dt = DateTime::createFromFormat($fmt,
  $s);
install Date::Parse
use Time::Local;
use Date::Parse;
 
$s = "2011-05-03 10:00:00";
$fmt = "%Y-%m-%d %H:%M:%S";
@tm = strptime($s, $fmt);
$t = timelocal(@tm);
from datetime import datetime
 
s = "2011-05-03 10:00:00"
fmt = "%Y-%m-%d %H:%M:%S"
t = datetime.stptime(s, fmt)
require 'date'
 
s = "2011-05-03 10:00:00"
fmt = "%Y-%m-%d %H:%M:%S"
t = Date.strptime(s, fmt).to_time
parse date $t = strtotime("July 7, 1999"); install Date::Parse
use Date::Parse;
 
$t = str2time('July 7, 1999');
install python-dateutil
import dateutil.parser
 
s = 'July 7, 1999'
t = dateutil.parser.parse(s)
s = 'July 7, 1999'
t = Date.parse(s).to_time
date subtraction DateInterval object if diff method used:
$fmt = "Y-m-d H:i:s";
$s = "2011-05-03 10:00:00";
$then = DateTime::createFromFormat($fmt, $s);
$now = new DateTime("now");
$interval = $now->diff($then);
Unix epoch values yield integer time difference in seconds datetime.timedelta object Float containing time difference in seconds
add time duration $now = new DateTime("now");
$now->add(new DateInterval("PT10M3S");
$now = time;
$now += 10 * 60 + 3;
import datetime
 
d = datetime.timedelta(
  minutes=10,
  seconds=3)
t = datetime.datetime.now + d
require 'date/delta'
 
s = '10 min, 3 s'
d = Date::Delta.parse(s).in_secs
t = Time.now + d
to unix epoch, from unix epoch $dt->getTimestamp();
$dt2 = new DateTime();
$dt2->setTimestamp(1304442000);
use Time::Local;
 
$t = timelocal(@tm);
@tm2 = localtime(1304442000);
from datetime import datetime
 
int(t.strftime("%s"))
datetime.fromtimestamp(1312604983)
t.to_i
Time.at(1312604983)
timezone name; offset from UTC; is daylight savings? $dtz = date_timezone_get($dt);
timezone_name_get($dtz);
date_offset_get($dt) / 3600;
$dt->format("I");
install DateTime
use DateTime;
use DateTime::TimeZone;
 
$dt = DateTime->now();
$tz = DateTime::TimeZone->new(
  name=>"local");
 
$tz->name;
$tz->offset_for_datetime($dt) /
  3600;
$tz->is_dst_for_datetime($dt);
import time
 
tm = time.localtime()
  
time.tzname[tm.tm_isdst]
(time.timezone / -3600) + tm.tm_isdst
tm.tm_isdst
t.zone
t.utc_offset / 3600
t.dst?
microseconds list($frac, $sec) = explode(" ",
  microtime());
$usec = $frac * 1000 * 1000;
use Time::HiRes qw(gettimeofday);
 
($sec, $usec) = gettimeofday;
t.microsecond t.usec
sleep a float argument will be truncated to an integer:
sleep(1);
a float argument will be truncated to an integer:
sleep 1;
import time
 
time.sleep(0.5)
sleep(0.5)
timeout use set_time_limit to limit execution time of the entire script; use stream_set_timeout to limit time spent reading from a stream opened with fopen or fsockopen eval {
  $SIG{ALRM}= sub {die "timeout!";};
  alarm 5;
  sleep 10;
};
alarm 0;
import signal
import time
 
class Timeout(Exception): pass
 
def timeout_handler(signo, fm):
  raise Timeout()
signal.signal(signal.SIGALRM,
  timeout_handler)
 
try:
  signal.alarm(5)
  time.sleep(10)
except Timeout:
  pass
signal.alarm(0)
require 'timeout'
 
begin
  Timeout.timeout(5) do
    sleep(10)
  end
rescue Timeout::Error
end
arrays
php perl python ruby
literal
 
$a = array(1,2,3,4); @a = (1,2,3,4); a = [1,2,3,4] a = [1,2,3,4]
quote words
 
@a = qw(foo bar baz); a = 'foo bar baz'.split() a = %w(foo bar baz)
size
 
count($a) $#a + 1 or
scalar(@a)
len(a) a.size
a.length # same as size
lookup
 
$a[0] $a[0] a[0] a[0]
update
 
$a[0] = 'foo'; $a[0] = 'foo'; a[0] = 'foo' a[0] = 'foo'
out-of-bounds behavior $a = array();
evaluates as NULL:
$a[10];
increases array size to one:
$a[10] = 'foo';
@a = ();
evaluates as undef:
$a[10];
increases array size to 11:
$a[10] = 'foo';
a = []
raises IndexError:
a[10]
raises IndexError:
a[10] = 'foo'
a = []
evaluates as nil:
a[10]
increases array size to 11:
a[10] = 'foo'
index of array element $a = array('x','y','z');
$i = array_search('y', $a);
use List::Util 'first';
@a = qw(x y z);
$i = first {$a[$_] eq 'y'} (0..$#a);
a = ['x','y','z']
i = a.index('y')
a = ['x','y','z']
i = a.index('y')
slice
 
# 3rd arg is length of slice:
array_slice($a,1,2)
@a[1..2] a[1:3] a[1..2]
slice to end
 
array_slice($a, 1) @a[1..$#a] a[1:] a[1..-1]
manipulate back
 
$a = array(6,7,8);
array_push($a, 9);
array_pop($a);
@a = (6,7,8);
push @a, 9;
pop @a;
a = [6,7,8]
a.append(9)
a.pop()
a = [6,7,8]
a.push(9)
a << 9 # same as push
a.pop
manipulate front
 
$a = array(6,7,8);
array_unshift($a, 5);
array_shift($a);
@a = (6,7,8);
unshift @a, 5;
shift @a;
a = [6,7,8]
a.insert(0,5)
a.pop(0)
a = [6,7,8]
a.unshift(5)
a.shift
concatenate $a = array(1,2,3);
$a2 = array_merge($a,array(4,5,6));
$a = array_merge($a,array(4,5,6));
@a = (1,2,3);
@a2 = (@a,(4,5,6));
push @a, (4,5,6);
a = [1,2,3]
a2 = a + [4,5,6]
a.extend([4,5,6])
a = [1,2,3]
a2 = a + [4,5,6]
a.concat([4,5,6])
address copy, shallow copy, deep copy $a = array(1,2,array(3,4));
$a2 =& $a;
none
$a4 = $a;
@a = (1,2,[3,4]);
$a2 = \@a;
@a3 = @a;

use Clone qw(clone);
$a4 = clone(\@a);
a = [1,2,[3,4]]
a2 = a
a3 = list(a)

import copy
a4 = copy.deepcopy(a)
a = [1,2,[3,4]]
a2 = a
a3 = a.dup
a4 = Marshal.load(Marshal.dump(a))
arrays as function arguments parameter contains deep copy each element passed as separate argument; use reference to pass array as single argument parameter contains address copy parameter contains address copy
iteration
 
foreach (array(1,2,3) as $i) {
  echo "$i\n";
}
for $i (1 2 3) { print "$i\n" } for i in [1,2,3]:
  print(i)
[1,2,3].each { |i| puts i }
indexed iteration $a = array('foo','bar','baz');
foreach ($a as $i => $s) {
  echo "$s at index $i\n";
}
my @a = ('foo','bar','baz');
for my $i (0..$#a) {
  print "$a[$i] at index $i\n";
};
for i, s in enumerate(['foo','bar','baz']):
  print("%s at index %d" % (s, i))
a = ['foo','bar','baz']
a.each_with_index do |s,i|
  puts "#{s} at index #{i}"
end
iterate over range not efficient; use C-style for loop for $i (1..1_000_000) {
  code
}
for i in xrange(1, 1000001):
  code
(1..1_000_000).each do |i|
  code
end
instantiate range as array $a = range(1, 10); @a = 1..10; a = range(1, 11) a = (1..10).to_a
sort $a = array(3,1,4,2);
none
sort($a);
@a = (3,1,4,2);
sort @a;
@a = sort @a;
sort { $a <=> $b } @a;
a = [3,1,4,2]
sorted(a)
a.sort()
a = [3,1,4,2]
a.sort
a.sort!
a.sort { |m,n| m <=> n}
reverse $a = array(1,2,3);
array_reverse($a);
$a = array_reverse($a);
@a = (1,2,3);
reverse @a;
@a = reverse @a;
a = [1,2,3]
a[::-1]
a.reverse()
a = [1,2,3]
a.reverse
a.reverse!
membership
 
in_array(7, $a) scalar(grep { 7 == $_ } @a) 7 in a a.include?(7)
intersection
 
$a = array(1,2);
$b = array(2,3,4)
array_intersect($a, $b)
set.intersection(set([1,2]),
  set([2,3,4]))
[1,2] & [2,3,4]
union
 
set.union(set([1,2]),set([2,3,4])) [1,2] | [2,3,4]
map
 
$t2 = create_function('$x', 'return $x*$x;')
array_map($t2, array(1,2,3))
map { $_ * $_ } (1,2,3) map(lambda x: x * x, [1,2,3])
# or use list comprehension:
[x*x for x in [1,2,3]]
[1,2,3].map { |o| o*o }
filter
 
$gt1 = create_function('$x','return $x>1;');
array_filter( array(1,2,3), $gt1)
grep { $_ > 1 } (1,2,3) filter(lambda x: x > 1,[1,2,3])
# or use list comprehension:
[x for x in [1,2,3] if x > 1]
[1,2,3].select { |o| o > 1 }
reduce
 
$add = create_function('$x,$y','return $x+$y;');
array_reduce(array(1,2,3),$add,0)
reduce { $x + $y } 0, (1,2,3) # import needed in python 3 only
import reduce from functools
reduce(lambda x,y:x+y,[1,2,3],0)
[1,2,3].inject(0) { |m,o| m+o }
universal test
 
none, use array_filter none, use grep all(i%2 == 0 for i in [1,2,3,4]) [1,2,3,4].all? {|i| i.even? }
existential test
 
none, use array_filter none, use grep any(i%2 == 0 for i in [1,2,3,4]) [1,2,3,4].any? {|i| i.even? }
shuffle and sample $a = array(1, 2, 3, 4);
shuffle($a);
none
use List::Util 'shuffle';
@a = (1, 2, 3, 4);
shuffle(@a);
none
from random import shuffle, sample
a = [1, 2, 3, 4]
shuffle(a)
sample(a, 2)
[1, 2, 3, 4].shuffle
ruby 1.9:
[1, 2, 3, 4].sample(2)
zip
 
none none zip([1,2,3],['a','b','c']) [1,2,3].zip(['a','b','c'])
dictionaries
php perl python ruby
literal
 
$d = array('t' => 1, 'f' => 0); %d = ( 't' => 1, 'f' => 0 ); d = { 't':1, 'f':0 } d = { 't' => 1, 'f' => 0 }
size
 
count($d) scalar(keys %d) len(d) d.size
d.length # same as size
lookup
 
$d['t'] $d{'t'} d['t'] d['t']
out-of-bounds behavior
 
$d = array();
evaluates as NULL:
$d['foo'];
adds key/value pair:
$d['foo'] = 'bar';
%d = ();
evaluates as undef:
$d{'foo'};
adds key/value pair:
$d{'foo'} = 'bar';
d = {}
raises KeyError:
d['foo']
adds key/value pair:
d['foo'] = 'bar'
d = {}
evaluates as nil:
d['foo']
adds key/value pair:
d['foo'] = 'bar'
is key present
 
array_key_exists('y', $d); exists($d{'y'}) 'y' in d d.has_key?('y')
delete entry $d = array(1 => 't', 0 => 'f');
unset($d[1]);
%d = ( 1 => 't', 0 => 'f' );
delete $d{1};
d = {1: True, 0: False}
del d[1]
d = {1 => true, 0 => false}
d.delete(1)
merge $d1 = array('a'=>1, 'b'=>2);
$d2 = array('b'=>3, 'c'=>4);
$d1 = array_merge($d1, $d2);
%d1 = (a=>1, b=>2);
%d2 = (b=>3, c=>4);
@d1{keys %d2} = values %d2;
d1 = {'a':1, 'b':2}
d2 = {'b':3, 'c':4}
d1.update(d2)
d1 = {'a'=>1, 'b'=>2}
d2 = {'b'=>3, 'c'=>4}
d1.merge!(d2)
invert $to_num = array('t'=>1, 'f'=>0);
$to_let = array_flip($to_num);
%to_num = (t=>1, f=>0);
%to_let = reverse %to_num;
to_num = {'t':1, 'f':0}
a = [[v,k] for k,v in to_num.items()]
to_let = dict(a)
to_num = {'t'=>1, 'f'=>0}
to_let = to_num.invert
iteration
 
foreach ($d as $k => $v ) { while ( ($k, $v) = each %d ) { for k,v in d.iteritems():
  code
d.each { |k,v| code }
keys and values as arrays array_keys($d)
array_values($d)
keys %d
values %d
d.keys()
d.values()
d.keys
d.values
default value class CountArray extends ArrayObject {
  public function offsetExists($i) {
    return true;
  }
  public function offsetGet($i) {
    if(!parent::offsetExists($i)) {
      parent::offsetSet($i, 0);
    }
    return parent::offsetGet($i);
  }
}
$counts = new CountArray();
define a tied hash class CountDict(dict):
  def __missing__(self, k):
    return 0
 
counts = CountDict()
counts = Hash.new do |h,k|
  h[k] = 0
end
functions
php perl python ruby
function declaration
 
function add($a, $b) {
  return $a + $b;
}
sub add { $_[0] + $_[1] } def add(a,b):
  return a+b
def add(a,b)
  a+b
end
function invocation functions are case insensitive:
ADD(3,7);
add(1,2); add(1,2) add(1,2)
missing argument
 
set to NULL with warning set to undef raises TypeError raises ArgumentError
default value
 
function my_log($x, $base=10) { none def log(x,base=10): def log(x,base=10)
arbitrary number of arguments function add() {
  return array_sum(func_get_args());
}
@_ contains all values def add(first,*rest):
  if not rest:
    return first
  else:
    return first+add(*rest)
def add(first, *rest)
  if rest.empty?
    first
  else
    first + add(*rest)
  end
end
named parameter definition
 
none none def f(**d): def f(h)
named parameter invocation
 
none none f(eps=0.01) f(:eps => 0.01)
pass number or string by reference
 
function foo(&$x, &$y) {
  $x += 1;
  $y .= 'ly';
}

$n = 7;
$s = 'hard';
foo($n, $s);
sub foo {
  $_[0] += 1;
  $_[1] .= 'ly';
}

my $n = 7;
my $s = 'hard';
foo($n, $s);
not possible not possible
pass array or dictionary by reference
 
function foo(&$x, &$y) {
  $x[2] = 5;
  $y['f'] = -1;
}

$a = array(1,2,3);
$d = array('t'=>1,'f'=>0);
foo($a, $d);
sub foo {
  $_[0][2] = 5;
  $_[1]{'f'} = -1;
}

my @a = (1,2,3);
my %d = ('t'=> 1, 'f' => 0);
foo(\@a, \%d);
def foo(x, y):
  x[2] = 5
  y['f'] = -1

a = [1,2,3]
d = {'t':1, 'f':0}
foo(a, d)
def foo(x, y)
  x[2] = 5
  y['f'] = -1
end

a = [1,2,3]
d = {'t'=> 1, 'f' => 0 }
foo(a, d)
return value
 
return arg or NULL return arg or last expression evaluated return arg or None return arg or last expression evaluated
multiple return values
 
function first_and_second(&$a) {
  return array($a[0], $a[1]);
}
$a = array(1,2,3);
list($x, $y) =
  first_and_second($a);
sub first_and_second {
  return ($_[0], $_[1]);
}
@a = (1,2,3);
($x, $y) = first_and_second(@a);
def first_and_second(a):
  return a[0], a[1]

x, y = first_and_second([1,2,3])
def first_and_second(a)
  return a[0], a[1]
end
x, y = first_and_second([1,2,3])
lambda declaration
 
$f = create_function('$x','return $x*$x;'); $f = sub { $_[0] * $_[0] } f = lambda x: x * x f = lambda { |x| x * x }
lambda invocation
 
$f(2) $f->(2) f(2) f.call(2)
function with private state function counter() {
  static $i = 0;
  return ++$i;
}
echo counter();
{
  my $i = 0;
  sub counter() { ++$i }
}
print counter() . "\n";
# state not private:
def counter():
  counter.i += 1
  return counter.i

counter.i = 0
print(counter())
none
closure function make_counter() {
  $i = 0;
  return function () use (&$i) {
    return ++$i;
  };
}
$nays = make_counter();
echo $nays();
sub make_counter() {
  my $i = 0;
  return sub() { ++$i };
}
my $nays = make_counter();
print $nays->() . "\n"
# python 3:
def make_counter():
  i = 0
  def counter():
    nonlocal i
    i += 1
    return i
  return counter

nays = make_counter()
def make_counter()
  i = 0
  return lambda { i +=1; i }
end
nays = make_counter
puts nays.call
generator none none def make_counter():
  i = 0
  while True:
    i += 1
    yield(i)
nays = make_counter()
print(nays.next())
# ruby 1.9:
def make_counter()
  return Fiber.new do
    i = 0
    while true
      i += 1
      Fiber.yield i
    end
  end
end
nays = make_counter
puts nays.resume
execution control
php perl python ruby
if
 
if ( 0 == $n ) {
  echo "no hits\n";
} elseif ( 1 == $n ) {
  echo "one hit\n";
} else {
  echo "$n hits\n";
}
if ( 0 == $n ) {
  print "no hits\n"
} elsif ( 1 == $n ) {
  print "1 hit\n"
} else {
  print "$n hits\n"
}
if 0 == n:
  print("no hits")
elif 1 == n:
  print("1 hit")
else:
  print(str(n) + " hits")
if n == 0
  puts "no hits"
elsif 1 == n
  puts "1 hit"
else
  puts "#{n} hits"
end
while
 
while ( $i < 100 ) { $i++; } while ( $i < 100 ) { $i++ } while i < 100:
  i += 1
while i < 100 do
  i += 1
end
break, continue, redo
 
break continue none last next redo break continue none break next redo
for
 
for ($i = 1; $i <= 10; $i++) {
  echo "$i\n";
}
for ( $i=0; $i <= 10; $i++ ) {
  print "$i\n";
}
none none
range iteration
 
foreach (range(1,10) as $i) {
  echo "$i\n";
}
for $i (1..10) { print "$i\n" } for i in range(1,11):
  print(i)
(1..10).each { |i| puts i }
statement modifiers
 
none print "positive\n" if $i > 0;
print "nonzero\n" unless $i == 0;
none puts 'positive' if i > 0
puts 'nonzero' unless i == 0
raise exception
 
throw new Exception("bad arg"); die "bad arg"; raise Exception("bad arg") # raises RuntimeError
raise "bad arg"
catch exception
 
try {
  risky();
} catch (Exception $e) {
  echo 'risky failed: ',
    $e->getMessage(), "\n";
}
eval { risky };
if ($@) {
  print "risky failed: $@\n";
}
try:
  risky()
except:
  print("risky failed")
# catches StandardError
begin
  risky
rescue
  print "risky failed: "
  puts $!.message
end
global variable for last exception raised none $EVAL_ERROR: $@
$OS_ERROR: $!
$CHILD_ERROR: $?
none last exception: $!
backtrace array of exc.: $@
exit status of child: $?
define exception class Bam extends Exception {
  function __construct() {
    parent::__construct("bam!");
  }
}
none class Bam(Exception):
  def __init__(self):
    super(Bam, self).__init__("bam!")
class Bam < Exception
  def initialize
    super("bam!")
  end
end
catch exception by type and assign to variable try {
  throw new Bam;
} catch (Bam $e) {
  echo $e->getMessage(), "\n";
}
none try:
  raise Bam()
except Bam as e:
  print(e)
begin
  raise Bam.new
rescue Bam => e
  puts e.message
end
finally/ensure
 
none none try:
  acquire_resource()
  risky()
finally:
  release_resource()
begin
  acquire_resource
  risky
ensure
  release_resource
end
uncaught exception behavior
 
stderr and exit stderr and exit stderr and exit
start thread
 
none use threads;
$f = sub { sleep 10 };
$t = threads->new($f);
class sleep10(threading.Thread):
  def run(self):
    time.sleep(10)
t = sleep10()
t.start()
t = Thread.new { sleep 10 }
wait on thread
 
none $t->join; t.join() t.join
environment and i/o
php perl python ruby
external command
 
exec('ls'); system('ls'); import os
os.system('ls')
system('ls')
backticks
 
exec('ls', $out = array());
$out
`ls`; import os
os.popen('ls').read()
`ls`
command line args, script name
 
count($argv)
$argv[0] $argv[1]
$_SERVER["SCRIPT_NAME"]
$#ARGV + 1
$ARGV[0] $ARGV[1]
$0
import sys
len(sys.argv)-1
sys.argv[1] sys.argv[2]
sys.argv[0]
ARGV.size
ARGV[0] ARGV[1]
$0
print to standard out
 
echo "hi world\n"; print "hi world\n"; print("hi world") puts "hi world"
standard file handles
 
$stdin = fopen('php://stdin','r');
$stdout = fopen('php://stdout','w');
$stderr = fopen('php://stderr','w');
STDIN STDOUT STDERR import sys
sys.stdin sys.stdout sys.stderr
$stdin $stdout $stderr
open file
 
$f = fopen('/etc/hosts','r'); open FILE, '/etc/hosts'; f = open('/etc/hosts') f = File.open('/etc/hosts') or
File.open('/etc/hosts') { |f|
open file for writing
 
$f = fopen('/tmp/php_test','w'); open FILE, ">/tmp/perl_test"; f = open('/tmp/test','w') f = File.open('/tmp/test','w') or
File.open('/tmp/test','w') { |f|
close file
 
fclose($f); close FILE; f.close() f.close
read line
 
$line = fgets($f); $line = <FILE> f.readline() f.gets
iterate over a file by line
 
while (!feof($f)) {
  $line = fgets($f);
while ($line = <FILE>) { for line in f: f.each do |line|
chomp
 
chop($line); chomp $line; line = line.rstrip('\r\n') line.chomp!
read entire file into array or string $a = file('/etc/hosts');
$s = file_get_contents('/etc/hosts');
@a = <FILE>;
$/ = undef;
$s = <FILE>;
a = f.readlines()
s = f.read()
a = f.lines.to_a
s = f.read
write to file
 
fwrite($f, 'hello'); print FILE "hello"; f.write('hello') f.write('hello')
flush file
 
use IO::Handle;
FILE->flush();
f.flush() f.flush
environment variable
 
getenv('HOME') $ENV{'HOME'} import os
os.getenv('HOME')
ENV['HOME']
exit
 
exit 0; exit 0; import sys
sys.exit(0)
exit(0)
set signal handller
 
$SIG{INT} = sub {
  die "exiting…\n";
};
import signal
def handler(signo, frame):
  print("exiting…")
  exit -1
signal.signal(signal.SIGINT, handler)
Signal.trap("INT", lambda { |signo| puts "exiting…"; exit })
libraries and modules
php perl python ruby
load library
 
require_once('foo.php'); require 'Foo.pm'; # or
require Foo; # or
use Foo;
import foo require 'foo' # or
require 'foo.rb'
reload library
 
require('foo.php'); do 'Foo.pm'; reload(foo) load 'foo.rb'
library path
 
$o = ini_get('include_path');
$n = $o . ':/some/path';
ini_set('include_path', $n);
push @INC, '/some/path'; import sys
sys.path.append('/some/path')
$: << '/some/path'
library path environment variable none PERL5LIB PYTHONPATH RUBYLIB
library path command line option none -I none -I
main in library unless (caller) {
  code
}
if __name__ == "__main__":
  code
if $0 == __FILE__
  code
end
module declaration
 
namespace Foo; package Foo;
require Exporter;
our @ISA = ("Exporter");
our @EXPORT_OK = ('bar', 'baz');
put declarations in foo.py class Foo or module Foo
submodule declaration namespace Foo\Bar; package Foo::Bar; create directory foo in library path containing file bar.py module Foo::Bar or
module Foo
  module Bar
module separator
 
\Foo\Bar\baz(); Foo::Bar::baz(); foo.bar.baz() Foo::Bar.baz
import module
 
none, but a long module name can be shortened # imports symbols in @EXPORT:
use Foo;
from foo import *
import definitions
 
only class names can be imported # bar and baz must be in
# @EXPORT or @EXPORT_OK:

use Foo ('bar', 'baz');
from foo import bar, baz none
managing multiple installations $ virtualenv -p /usr/bin/python foo
$ source foo/bin/activate
list installed packages, install a package
 
$ pear list
$ pear install Math_BigInteger
$ perldoc perllocal
$ cpan -i Moose
$ pip freeze
$ pip install jinja2
$ gem list
$ gem install rails
objects
php perl python ruby
define class
 
class Int {
  public $value;
  function __construct($int=0) {
    $this->value = $int;
  }
}
package Int;
use Moose;
has 'value' => ( is => 'rw' );
around BUILDARGS => sub {
  my $orig = shift;
  my $class = shift;
  my $v = $_[0] || 0;
  $class->$orig(value => $v);
};
no Moose;
class Int:
  def __init__(self, v=0):
    self.value = v
class Int
  attr_accessor :value
  def initialize(i=0)
    @value = i
  end
end
create object
 
$i = new Int(); my $i = new Int(); # or
my $i = Int->new();
i = Int() i = Int.new
get and set attribute
 
$v = $i->value;
$i->value = $v+1;
my $v = $i->value;
$i->value($v+1);
v = i.value
i.value = v+1
v = i.value
i.value = v+1
instance variable accessibility must be declared private by default public; attributes starting with underscore private by convention private by default; use attr_reader, attr_writer, attr_accessor to make public
define method
 
function plus($i) {
  return $this->value + $i;
}
# in package:
sub plus {
  my $self = shift;
  $self->value + $_[0];
}
def plus(self,v):
  return self.value + v
def plus(i)
  value + i
end
invoke method
 
$i->plus(7) $i->plus(7) i.plus(7) i.plus(7)
destructor
 
function __destruct() {
  echo "bye, $this->value\n";
}
# in package:
sub DEMOLISH {
  my $self = shift;
  my $v = $self->value;
  print "bye, $v\n";
}
def __del__(self):
  print("bye, %", self.value)
val = i.value
ObjectSpace.define_finalizer(int) {
  puts "bye, #{val}"
}
method missing
 
function __call($name, $args) {
  $argc = count($args);
  echo "no def: $name " .
    "arity: $argc\n";
}
# in package:
our $AUTOLOAD;
sub AUTOLOAD {
  my $self = shift;
  my $argc = scalar(@_);
  print "no def: $AUTOLOAD"
    . " arity: $argc\n";
}
def __getattr__(self, name):
  s = "no def: "+name+" arity: %d"
  return lambda *a: print(s % len(a))
def method_missing(name, *a)
  puts "no def: #{name}" +
    " arity: #{a.size}"
end
inheritance
 
class Counter extends Int {
  private static $instances = 0;
  function __construct($int=0) {
    Counter::$instances += 1;
    parent::__construct($int);
  }
  function incr() {
    $this->value++;
  }
  static function getInstances() {
    return $instances;
  }
}
package Counter;
use Moose;
extends 'Int';
my $instances = 0;
sub BUILD {
  $instances += 1;
}
sub incr {
  my $self = shift;
  my $v = $self->value;
  $self->value($v + 1);
}
sub instances {
  $instances;
}
no Moose;
class Counter(Int):
  instances = 0
  def __init__(self, v=0):
    Counter.instances += 1
    Int.__init__(self, v)
  def incr(self):
    self.value += 1
class Counter < Int
  @@instances = 0
  def initialize
    @@instances += 1
    super
  end
  def incr
    self.value += 1
  end
  def self.instances
    @@instances
  end
end
invoke class method
 
Counter::getInstances() Counter::instances(); Counter.instances Counter.instances
reflection
php perl python ruby
class
 
get_class($a) ref $a type(a) a.class
has method?
 
method_exists($a, 'reverse') $a->can('reverse') hasattr(a,'reverse') a.respond_to?('reverse')
message passing
 
for ($i = 1; $i <= 10; $i++) {
  call_user_func(array($a,
    "phone$i"), NULL);
}
for $i (0..10) {
  $meth = "phone$i";
  $a->$meth(undef);
}
for i in range(1,10):
  getattr(a,"phone"+str(i))(None)
(1..9).each do |i|
  a.send("phone#{i}="nil)
}
eval
 
while(<>) {
  print ((eval), "\n");
}
while True:
  print(eval(sys.stdin.readline()))
loop do
  puts eval(gets)
end
methods
 
$class = ref($a);
keys eval "%${class}::";
[m for m in dir(a) if callable(getattr(a,m))] a.methods
attributes
 
keys %$a; dir(a) a.instance_variables
pretty print
 
$d = array('foo'=>1, 'bar'=>array(2,3));
print_r($d);
require 'dumpvar.pl';
%d = ('foo'=>1, 'bar'=>[2, 3]);
dumpValue(\%d);
import pprint
d = {'foo':1, 'bar':[2,3] }
pprint.PrettyPrinter().pprint(d)
require 'pp'
d = { 'foo'=>1, 'bar'=>[2,3] }
pp d
source line number and file name __LINE__
__FILE__
__LINE__
__FILE__
import inspect
c = inspect.currentframe()
c.f_lineno
c.f_code.co_filename
__LINE__
__FILE__
check syntax
 
$ php -l foo.php $ perl -c foo.pl # precompile to bytecode:
import py_compile
py_compile.compile("foo.py")
$ ruby -c foo.rb
flags for stronger and strongest warnings none $ perl -w foo.pl
$ perl -W foo.pl
$ python -t foo.py
$ python -3t foo.py
$ ruby -w foo.rb
$ ruby -W2 foo.rb
web
php perl python ruby
http get
 
$h = 'http://www.google.com';
$ch = curl_init($h);
curl_setopt($ch,
  CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
curl_close($ch);
$output
require HTTP::Request;
require LWP::UserAgent;
$h = 'http://www.google.com';
$r =
  HTTP::Request->new(GET=>$h);
$ua = LWP::UserAgent->new;
$resp = $ua->request($r);
$resp->content()
import httplib
h = 'www.google.com'
f = httplib.HTTPConnection(h)
f.request("GET",'/')
f.getresponse().read()
require 'net/http'
h = 'www.google.com'
r = Net::HTTP.start(h, 80) do |f|
  f.get('/')
end
r.body
url encode/decode
 
urlencode("hello world");
urldecode("hello+world");
use CGI;
CGI::escape('hello world')
CGI::unescape('hello+world')
import urllib
urllib.quote_plus("hello world")
urllib.unquote_plus("hello+world")
require 'cgi'
CGI::escape('hello world');
CGI::unescape('hello+world');
build xml $x = '<a></a>';
$d = new SimpleXMLElement($x);
$d->addChild('b', 'foo');
echo $d->asXML();
# not ported to python 3
from xmlbuilder import XMLBuilder
builder = XMLBuilder()
with builder.a:
  with builder.b:
    builder << "foo"
print(str(builder))
# gem install builder
require 'builder'
builder = Builder::XmlMarkup.new
xml = builder.a do |child|
  child.b("foo")
end
puts xml
parse xml $x = '<a><b>foo</b></a>';
$d = simplexml_load_string($x);
foreach ($d->children() as $c) {
  break;
}
echo $c;
# download XML::Simple from CPAN:
use XML::Simple;
$xml = new XML::Simple;
$s = '<a><b>foo</b></a>';
$doc = $xml->XMLin($s);
print $doc->{'b'};
from xml.etree import ElementTree
xml = '<a><b>foo</b></a>'
doc = ElementTree.fromstring(xml)
print(doc[0].text)
require 'rexml/document'
xml = '<a><b>foo</b></a>'
doc = REXML::Document.new(xml)
puts doc[0][0].text
xpath $x = '<a><b><c>foo</c></b></a>';
$d = simplexml_load_string($x);
$n = $d->xpath('/a/b/c');
echo $n[0];
from xml.etree import ElementTree
xml = '<a><b><c>foo</c></b></a>'
doc = ElementTree.fromstring(xml)
node = doc.find("b/c")
print(node.text)
require 'rexml/document'
include REXML
xml = '<a><b><c>foo</c></b></a>'
doc = Document.new(xml)
node = XPath.first(doc,'/a/b/c')
puts node.text
json $a = array('t'=>1, 'f'=>0);
$s = json_encode($a);
$d = json_decode($s, TRUE);
# download JSON from CPAN:
use JSON;
$raw = { 't' => 1, 'f' => 0 };
$json = JSON->new->allow_nonref;
$s = $json->encode($raw);
$d = $json->decode($s);
import json
s = json.dumps({'t':1, 'f':0})
d = json.loads(s)
require 'json'
s = {'t'=> 1,'f'=> 0}.to_json
d = JSON.parse(s)
java interoperation
php perl python ruby
version
 
Jython 2.5.1 JRuby 1.4.0
repl
 
jython jirb
interpreter
 
jython jruby
compiler
 
none in 2.5.1 jrubyc
prologue
 
import java none
new
 
rnd = java.util.Random() rnd = java.util.Random.new
method
 
rnd.nextFloat() rnd.next_float
import
 
from java.util import Random
rnd = Random()
java_import java.util.Random
rnd = Random.new
non-bundled java libraries
 
import sys
sys.path.append('path/to/mycode.jar')
import MyClass
require 'path/to/mycode.jar'
shadowing avoidance
 
import java.io as javaio module JavaIO
  include_package "java.io"
end
to java array
 
import jarray
jarray.array([1,2,3],'i')
[1,2,3].to_java(Java::int)
java class subclassable?
 
yes yes
java class open?
 
no yes
__________________________________________ __________________________________________ __________________________________________ __________________________________________

General Footnotes

versions used

The versions used for testing code in the cheat sheet.

show version

How to get the version.

php:

The function phpversion() will return the version number as a string.

perl:

Also available in the predefined variable $], or in a different format in $^V and $PERL_VERSION.

python:

The following function will return the version number as a string:

import platform
platform.python_version()

ruby:

Also available in the global constant VERSION (ruby 1.8.7) or RUBY_VERSION (ruby 1.9.1).

interpreter

The customary name of the interpreter and how to invoke it.

php:

php -f will only execute portions of the source file within a <?php php code ?> tag as php code. Portions of the source file outside of such tags is not treated as executable code and is echoed to standard out.

If short tags are enabled, then php code can also be placed inside <? php code ?> and <?= php code ?> tags. <?= php code ?> is identical to <?php echo php code ?>.

repl

The customary name of the repl.

php:

Submit each line of code to php -a as <?= php code ?> to have the line executed as php code and the result displayed.

perl:

The perl repl lacks readline and does not save or display the result of an expression. Actually, 'perl -d' runs the perl debugger, and 'perl -e' runs code provided on the command line.

python:

The python repl saves the result of the last statement in _.

ruby:

irb saves the result of the last statement in _.

statement separator

How the parser determines the end of a statement.

php:

The ; is a separator and not a terminator. It is not required before a closing ?> tag of a php block.

perl:

In a script statements are separated by semicolons and never by newlines. However, when using 'perl -de 0', a newline terminates the statement.

python:

Newline does not terminate a statement when:

  • inside parens
  • inside list [] or dictionary {} literals

Python single quote '' and double quote "" strings cannot contain newlines except as the two character escaped form \n. Putting a newline in these strings results in a syntax error. There is however a multi-line string literal which starts and ends with three single quotes ''' or three double quotes: """.

A newline that would normally terminate a statement can be escaped with a backslash.

ruby:

Newline does not terminate a statement when:

  • inside single quotes '', double quotes "", backticks ``, or parens ()
  • after an operator such as + or , that expects another argument

Ruby permits newlines in array [] or hash literals, but only after a comma , or associator =>. Putting a newline before the comma or associator results in a syntax error.

A newline that would normally terminate a statement can be escaped with a backslash.

block delimiters

How blocks are delimited.

perl:

Curly brackets {} delimit blocks. They are also used for:

  • hash literal syntax which returns a reference to the hash: $rh = { 'true' => 1, 'false' => 0 }
  • hash value lookup: $h{'true'}, $rh->{'true'}
  • variable name delimiter: $s = "hello"; print "${s}goodbye";

python:

Python blocks begin with a line that ends in a colon. The block ends with the first line that is not indented further than the initial line. Python raises an IndentationError if the statements in the block that are not in a nested block are not all indented the same. Using tabs in Python source code is unrecommended and many editors replace them automatically with spaces. If the Python interpreter encouters a tab, it is treated as 8 spaces.

The python repl switches from a >>> prompt to a … prompt inside a block. A blank line terminates the block.

ruby:

Curly brackets {} delimit blocks. A matched curly bracket pair can be replaced by the do and end keywords. By convention curly brackets are used for one line blocks. The end keyword also terminates blocks started by def, class, or module.

Curly brackets are also used for hash literals, and the #{ } notation is used to interpolate expressions into strings.

assignment

How to assign a value to a variable.

perl:

Assignment operators have right precedence and evaluate to the right argument, so assignments can be chained:

$a = $b = 3;

python:

If the variable on the left does not exist, then it is created.

Assignment does not return a value and cannot be used in an expression. Thus, assignment cannot be used in a conditional test, removing the possibility of using assignment (=) in place of an equality test (==). Assignments can nevertheless be chained to assign multiple variables to the same value:

a = b = 3

ruby:

Assignment operators have right precedence and evaluate to the right argument, so they can be chained. If the variable on the left does not exist, then it is created.

parallel assignment

How to assign values to variables in parallel.

python:

The r-value can be a list or tuple:

nums = [1,2,3]
a,b,c = nums
more_nums = (6,7,8)
d,e,f = more_nums

Nested sequences of expression can be assigned to a nested sequences of l-values, provided the nesting matches. This assignment will set a to 1, b to 2, and c to 3:

(a,[b,c]) = [1,(2,3)]

This assignment raises a TypeError:

ruby:

The r-value can be an array:

nums = [1,2,3]
a,b,c = nums

swap

How to swap the values held by two variables.

compound assignment

Compound assignment operators mutate a variable, setting it to the value of an operation which takes the value of the variable as an argument.

First row: arithmetic operator assignment: addition, subtraction, multiplication, (float) division, integer division, modulus, and exponentiation.
Second row: string concatenation assignment and string replication assignment
Third row: logical operator assignment: and, or, xor
Fourth row: bit operator compound assignment: left shift, right shift, and, or, xor.

python:

Python compound assignment operators do not return a value and hence cannot be used in expressions.

increment and decrement

php:

The increment and decrement operators also work on strings. There are postfix versions of these operators which evaluate to the value before mutation:

$x = 1;
$x++;
$x--;

perl:

The increment and decrement operators also work on strings. There are postfix versions of these operators which evaluate to the value before mutation:

$x = 1;
$x++;
$x--;

ruby:

The Integer class defines succ, pred, and next, which is a synonym for succ.

The String class defines succ, succ!, next, and next!. succ! and next! mutate the string.

local variable declarations

How to declare variables which are local to the scope defining region which immediately contain them.

php:

Variables do not need to be declared and there is no syntax for declaring a local variable. If a variable with no previous reference is accessed, its value is NULL.

perl:

Variables don't need to be declared unless use strict is in effect.

If not initialized, scalars are set to undef, arrays are set to an empty array, and hashes are set to an empty hash.

Perl can also declare variables with local. These replace the value of a global variable with the same name, if any, for the duration of the enclosing scope, after which the old value is restored. local declarations became obsolete with the introduction of the my declaration introduced in Perl 5.

python:

A variable is created by assignment if one does not already exist. If the variable is inside a function or method, then its scope is the body of the function or method. Otherwise it is a global.

ruby:

Variables are created by assignment. If the variable does not have a dollar sign ($) or ampersand (@) as its first character then its scope is scope defining region which most immediately contains it.

A lower case name can refer to a local variable or method. If both are defined, the local variable takes precedence. To invoke the method make the receiver explicit: e.g. self.name. However, outside of class and modules local variables hide functions because functions are private methods in the class Object. Assignment to name will create a local variable if one with that name does not exist, even if there is a method name.

regions which define local scope

A list of regions which define a scope for the local variables they contain.

Local variables defined inside the region are only in scope while code within the region is executing. If the language does not have closures, then code outside the region has no access to local variables defined inside the region. If the language does have closures, then code inside the region can make local variables accessible to code outside the region by returning a reference.

A region which is top level hides local variables in the scope which contains it from the code it contains. A region can also be top level if the syntax requirements of the language prohibit from being placed inside another scope defining region.

A region is nestable if it can be placed inside another cope defining region, and if code in the inner region can access local variables in the outer region.

php:

Only function bodies and method bodies define scope. Function definitions can be nested, but when this is done lexical variables in the outer function are not visible to code in the body of the inner function.

Braces can be used to set off blocks of codes in a manner similar to the anonymous blocks of Perl. However, these braces do not define a scope. Local variables created inside the braces will be visible to subsequent code outside of the braces.

Local variables cannot be created in class bodies.

perl:

A local variable can be defined outside of any function definition or anonymous block, in which case the scope of the variable is the file containing the source code. In this way Perl resembles Ruby and contrasts with PHP and Python. In PHP and Python, any variable defined outside a function definition is global.

In Perl, when a region which defines a scope is nested inside another, then the inner region has read and write access to local variables defined in the outer region.

Note that the blocks associated with the keywords if, unless, while, until, for, and foreach are anonymous blocks, and thus any my declarations in them create variables local to the block.

python:

Only functions and methods define scope. Function definitions can be nested. When this is done, inner scopes have read access to variables defined in outer scopes. Attempting to write (i.e. assign) to a variable defined in an outer scope will instead result in a variable getting created in the inner scope.

ruby:

Note that though the keywords if, unless, case, while, and until each define a block which is terminated by an end keyword, none of these blocks have their own scope.

Anonymous functions can be created with the lambda keyword. Ruby anonymous blocks can be provided after a function invocation and are bounded by curly brackets { } or the do and end keywords. Both anonymous functions and anonymous blocks can have parameters which are specified at the start of the block within pipes. Here are some examples:

id = lambda { |x| x }

[3,1,2,4].sort { |a,b| a <=> b }

10.times do |i|
  print "#{i}..." 
end

In Ruby 1.8, the scope of the parameter of an anonymous block or function or block is local to the block or function body if the name is not already bound to a variable in the containing scope. However, if it is, then the variable in the containing scope will be used. This behavior was changed in Ruby 1.9 so that parameters are always local to function body or block. Here is an example of code which behaves differently under Ruby 1.8 and Ruby 1.9:

x = 3
id = lambda { |x| x }
id.call(7)
puts x # 1.8 prints 7; 1.9 prints 3

Ruby 1.9 also adds the ability mark variables as local, even when they are already defined in the containing scope. All such variables are listed inside the parameter pipes, separated from the parameters by a semicolon:

x = 3
noop = lambda { |; x| x = 15 } # bad syntax under 1.8
noop.call
# x is still 3

global variable

How to declare and access a variable with global scope.

php:

A variable is global if it is used at the top level (i.e. outside any function definition) or if it is declared inside a function with the global keyword. A function must use the global keyword to access the global variable.

perl:

Undeclared variables, which are permitted unless use strict is in effect, are global. If use strict is in effect, a global can be declared at the top level of a package (i.e. outside any blocks or functions) with the our keyword. A variable declared with my inside a function will hide a global with the same name, if there is one.

python:

A variable is is global if it is defined at the top level of a file (i.e. outside any function definition). Although the variable is global, it must be imported individuality or be prefixed with the module name prefix to be accessed from another file. To be accessed from inside a function or method it must be declared with the global keyword.

ruby:

A variable is global if it starts with a dollar sign: $.

static variable

How to create a variable which is private to a function but keeps state between invocations.

constant declaration

How to declare a constant.

php:

A constant can be declared inside a class:

class Math {
  const pi = 3.14;
}

Refer to a class constant like this:

Math::pi

ruby:

Capitalized variables contain constants and class/module names. By convention, constants are all caps and class/module names are camel case. The ruby interpreter does not prevent modification of constants, it only gives a warning. Capitalized variables are globally visible, but a full or relative namespace name must be used to reach them: e.g. Math::PI.

to-end-of-line comment

How to create a comment that ends at the next newline.

comment out multiple lines

How to comment out multiple lines.

python:

The triple single quote ''' and triple double quote """ syntax is a syntax for string literals.

null

The null literal.

null test

How to test if a variable contains null.

php:

$v == NULL does not imply that $v is NULL, since any comparison between NULL and a falsehood will return true. In particular, the following comparisons are true:

$v = NULL;
if ($v == NULL) { echo "true"; }
$v = 0;
if ($v == NULL) { echo "sadly true"; }
$v = '';
if ($v == NULL) { echo "sadly true"; }

perl:

$v == undef does not imply that $v is undef. Any comparison between undef and a falsehood will return true. The following comparisons are true:

$v = undef;
if ($v == undef) { print "true"; }
$v = 0;
if ($v == undef) { print "sadly true"; }
$v = '';
if ($v == undef) { print "sadly true"; }

undefined variable access

The result of attempting to access an undefined variable.

undefined test

Perl does not distinguish between unset variables and variables that have been set to undef. In perl, calling defined($a) does not result in a error if $a is undefined, even with the strict pragma.

Arithmetic and Logic Footnotes

true and false

php:

Any identifier which matches TRUE case-insensitive can be used for the TRUE boolean. Similarly for FALSE.

In general, PHP variable names are case-sensitive, but function names are case-insensitive.

When converted to a string for display purposes, TRUE renders as "1" and FALSE as "". The equality tests TRUE == 1 and FALSE == "" evaluate as TRUE but the equality tests TRUE === 1 and FALSE === "" evaluate as FALSE.

falsehoods

python:

Whether a object evaluates to True or False in a boolean context can be customized by implementing a __nonzero__ instance method for the class.

logical operators

Logical and, or, and not.

php:

&& || and ! have higher precedence than assignment and the ternary operator (?:). and, or, and xor have lower precedence than assignment and the ternary operator.

perl:

&& || and ! have higher precedence than assignment and the ternary operator (?:). and, or, and xor have lower precedence than assignment and the ternary operator.

conditional expression

How to write a conditional expression. A ternary operator is an operator which takes three arguments. Since

condition ? true value : false value

is the only ternary operator in C, it is unambiguous to refer to it as the ternary operator.

python:

The Python conditional expression comes from Algol.

comparison operators

Equality, inequality, greater than, less than, greater than or equal, less than or equal.

php:

Most of the comparison operators will convert a string to a number if the other operand is a number. Thus 0 == "0" is true. The operators === and !== do not perform this conversion, so 0 === "0" is false.

perl:

The operators: == != > < >= <= convert strings to numbers before performing a comparison. Many string evaluate as zero in a numeric context and are equal according to the == operator. To perform a lexicographic string comparison, use: eq, ne, gt, lt, ge, le.

convert from string, to string

How to convert string data to numeric data and vice versa.

php:

PHP converts a scalar to the desired type automatically and does not raise an error if the string contains non-numeric data. If the start of the string is not numeric, the string evaluates to zero in a numeric context.

perl:

Perl converts a scalar to the desired type automatically and does not raise an error if the string contains non-numeric data. If the start of the string is not numeric, the string evaluates to zero in a numeric context.

python:

float and int raise an error if called on a string and any part of the string is not numeric.

ruby:

to_i and to_f always succeed on a string, returning the numeric value of the digits at the start of the string, or zero if there are no initial digits.

arithmetic operators

The operators for addition, subtraction, multiplication, float division, integer division, modulus, and exponentiation.

integer division

How to get the integer quotient of two integers. How to get the integer quotient and remainder.

perl:

The integer pragma makes all arithmetic operations integer operations. Floating point numbers are truncated before they are used. Hence integer division could be performed with:

use integer;
my $a = 7 / 3;
no integer;

float division

How to perform floating point division, even if the operands might be integers.

arithmetic functions

Some arithmetic functions. Trigonometric functions are in radians unless otherwise noted. Logarithms are natural unless otherwise noted.

python:

Python also has math.log10. To compute the log of x for base b, use:

math.log(x)/math.log(b)

ruby:

Ruby also has Math.log2, Math.log10. To compute the log of x for base b, use

Math.log(x)/Math.log(b)

arithmetic truncation

How to truncate a float to the nearest integer towards zero; how to round a float to the nearest integer; how to find the nearest integer above a float; how to find the nearest integer below a float; how to take the absolute value.

perl:

The CPAN module Number::Format provides a round function. The 2nd argument specifies the number of digits to the right of the radix. The default is 2.

use Number::Format 'round';

round(3.14, 0);

min and max

How to get the min and max.

division by zero

What happens when division by zero is performed.

integer overflow

What happens when the largest representable integer is exceeded.

float overflow

What happens when the largest representable float is exceeded.

sqrt -2

The result of taking the square root of negative two.

rational numbers

How to create rational numbers and get the numerator and denominator.

ruby:

Require the library mathn and integer division will yield rationals instead of truncated integers.

complex numbers

python:

Most of the functions in math have analogues in cmath which will work correctly on complex numbers.

random integer, uniform float, normal float

How to generate a random integer between 0 and 99, include, float between zero and one in a uniform distribution, or a float in a normal distribution with mean zero and standard deviation one.

bit operators

The bit operators for left shift, right shift, and, inclusive or, exclusive or, and negation.

binary, octal, and hex literals

Binary, octal, and hex integer literals

base conversion

How to convert integers to strings of digits of a given base. How to convert such strings into integers.

python

Python has the functions bin, oct, and hex which take an integer and return a string encoding the integer in base 2, 8, and 16:

bin(42)
oct(42)
hex(42)

String Footnotes

string literal

The syntax for string literals.

newline in literal

Whether newlines are permitted in string literals.

python:

Newlines are not permitted in single quote and double quote string literals. A string can continue onto the following line if the last character on the line is a backslash. In this case, neither the backslash nor the newline are taken to be part of the string.

Triple quote literals, which are string literals terminated by three single quotes or three double quotes, can contain newlines:

'''This is
two lines'''

"""This is also
two lines"""

backslash escapes

Backslash escape sequences for inserting special characters into string literals.

python:

Before python 3, it was possible to enter a character by Unicode point using the following syntax:

u'\u03bb'

variable interpolation

How to interpolate variables into strings.

python:

Python lacks interpolating quotes. Except for the fact that they can contain single quotes, double quotes are identical to single quotes.

custom delimiters

How to specify custom delimiters for single and double quoted strings. These can be used to avoid backslash escaping. If the left delimiter is (, [, or { the right delimiter must be ), ], or }, respectively.

sprintf

How to create a string using a printf style format.

python:

Escape curly braces by doubling:

'to insert parameter {0} into a format, use {{{0}}}'.format(3)

here document

Here documents are strings terminated by a custom identifier. They perform variable substitution and honor the same backslash escapes as double quoted strings.

perl:

Put the custom identifer in single quotes to prevent variable interpolation and backslash escape interpretation:

s = <<'EOF';
Perl code uses variables with dollar
signs, e.g. $var
EOF

python:

Python lacks variable interpolation in strings. Triple quotes honor the same backslash escape sequences as regular quotes,
so triple quotes can otherwise be used like here documents:

s = '''here document
there computer
'''

ruby:

Put the customer identifier in single quotes to prevent variable interpolation and backslash escape interpretation:

s = <<'EOF'
Ruby code uses #{var} type syntax
to interpolate variables into strings.
EOF

concatenate

The string concatenation operator.

replicate

The string replication operator.

split

How to split a string containing a separator into an array of substrings.

ruby:

The argument to split can be a string or regular expression. A 2nd argument will put a limit on the number of elements in the array; the last element will contain the reaminder of the string. To split a string into an array of single character strings, use

"abcdefg".split('')

join

How to concatenate the elements of an array into a string with a separator.

case manipulation

How to put a string into all caps or all lower case letters. How to capitalize the first letter of a string.

strip

How to remove whitespace from the ends of a string.

pad on right, on left

How to pad the edge of a string with spaces so that it is a prescribed length.

length

How to get the length in characters of a string.

index of substring

How to find the index of the leftmost occurrence of a substring in a string.

extract substring

How to extract a substring from a string by index.

extract character

How to extract a character from a string by its index.

chr and ord

Converting characters to ASCII codes and back.

The languages in this reference sheet do not have character literals, so characters are represented by strings of length one.

character count

how to count the number times a character occurs in a string

perl:

The translate characters tr operator returns the number of characters replaced. Normally it performs a destructive operation on the string, but not if the second half of the translation specification is empty.

character translation

How to apply a character mapping to a string.

regexp match

How to test whether a string matches a regular expression.

match, prematch, postmatch

substring matches

scan

single substitution

perl:

The =~ operator performs the substitution in place on the string, and returns the number of substitutions performed.

python:

The 3rd argument of sub indicates the maximum number of substitutions to be performed. The default value is zero, in which case there is no limit to the number of substitutions performed.

ruby:

The sub operator returns a copy of the string with the substitution made, if any. The sub! performs the substitution on the original string and returns the modified string.

global substitution

How to replace all occurrences of a pattern in a string with a substitution.

perl:

The =~ operator performs the substitution in place on the string, and returns the number of substitutions performed.

ruby:

The gsub operator returns a copy of the string with the substitution made, if any. The gsub! performs the substitution on the original string and returns the modified string.

Date and Time Footnotes

In ISO 8601 terminology, a date specifies a day in the Gregorian calendar and a time does not contain date information; it merely specifies a time of day. A data type which combines both date and time information is probably more useful than one which contains just date information or just time information, and it is unfortunate that ISO 8601 doesn't provide a name for this entity. The word timestamp often gets used to denote a combined date and time. PHP and Python use the compound noun datetime for combined date and time values.

An interesting property of ISO 8601 dates, times, and date/time combinations is that they are correctly ordered by a lexical sort on their string representations. This is because they are big-endian (the year is the leftmost element) and they used fixed-length fields for each term in the string representation.

The C standard library provides two methods for representing dates. The first is the UNIX epoch, which is the seconds since January 1, 1970 in UTC. If such a time were stored in a 32-bit signed integer, the rollover would happen on January 18, 2038.

The other method representing dates is the tm struct, a definition of which can be found on Unix systems in /usr/include/time.h:

struct tm {
        int     tm_sec;         /* seconds after the minute [0-60] */
        int     tm_min;         /* minutes after the hour [0-59] */
        int     tm_hour;        /* hours since midnight [0-23] */
        int     tm_mday;        /* day of the month [1-31] */
        int     tm_mon;         /* months since January [0-11] */
        int     tm_year;        /* years since 1900 */
        int     tm_wday;        /* days since Sunday [0-6] */
        int     tm_yday;        /* days since January 1 [0-365] */
        int     tm_isdst;       /* Daylight Savings Time flag */
        long    tm_gmtoff;      /* offset from CUT in seconds */
        char    *tm_zone;       /* timezone abbreviation */
};

Perl and Python both use and expose the tm struct of the standard library. In the case of Perl, the first nine values of the struct (up to the member tm_isdst) are put into an array. Python, meanwhile, has a module called time which is a thin wrapper to the standard library functions which operate on this struct. Here is how get a tm struct in Python:

import time

utc = time.gmtime(time.time())
t = time.localtime(time.time())

The tm struct is a low level entity, and interacting with it directly should be avoided. In the case of Python it is usually sufficient to use the datetime module instead. Avoiding the tm struct in Perl is a bit more difficult and might require downloading CPAN modules.

date/time type

The data type used to hold a combined date and time.

perl

Built in Perl functions work with either (1) scalars containing the Unix epoch as an integer or (2) arrays containing the first nine values of the standard C library tm struct. The modules Time::Local and Date::Parse can both be used to create scalars containing the Unix epoch.

CPAN provides the DateTime module which provides objects with functionality comparable to the DateTime objects of PHP and Python.

current date/time

How to get the combined date and time for the present moment in both local time and UTC.

local timezone

Do date/time values include timezone information. When a date/time value for the local time is created, how the local timezone is determined.

A date/time value can represent a local time but not have any timezone information associated with it.

On Unix systems processes determine the local timezone by inspecting the file /etc/localtime.

php:

The default timezone can also be set in the php.ini file.

date.timezone = "America/Los_Angeles"

Here is the list of timezones supported by PHP.

perl:

Although the tm struct from the standard library has a tm_zone member, the Perl tm array does not have a corresponding element.

strftime

How to format a timestamp as a string using the format notation of the strftime function from the standard C library. This same format notation is used by the Unix date command.

php:

PHP supports strftime but it also has its own time formatting system used by date, DateTime::format, and DateTime::createFromFormat. The letters used in the PHP time formatting system are described here.

strptime

How to parse a timestamp using the format notation of strptime function from the standard C library.

parse date

How to parse a date without providing a format string.

date subtraction

The data type that results when subtraction is performed on two combined date and time values.

perl

It is rarely useful to subtract arrays holding tm values as the arrays will first be converted to scalar values indicating their size.

add time duration

How to add a time duration to a timestamp.

A time duration can easily be added to a date/time value when the value is a Unix epoch value.

ISO 8601 distinguishes between a time interval, which is defined by two date/time endpoints, and a duration, which is the length of a time interval and can be defined by a unit of time such as '10 minutes'. A time interval can also be defined by date and time representing the start of the interval and a duration.

ISO 8601 defines notation for durations. This notation starts with a 'P' and uses a 'T' to separate the day and larger units from the hour and smaller units. Observing the location relative to the 'T' is important for interpreting the letter 'M', which is used for both months and minutes.

perl

The technique illustrated, namely using an arithmetic expression to calculate the length of a duration in seconds, is probably the most practical one when working in Perl. There is also the following CPAN module:

use Time::Interval;

$now = time;
$now += convertInterval( minutes=>10, seconds=>3, ConvertTo=>"seconds");

to unix epoch, from unix epoch

How to convert the native timestamp type to the Unix epoch which is the number of seconds since the start of January 1, 1970 UTC.

timezone name, offset from UTC, is daylight savings?

How to get time zone information: the name of the timezone, the offset in hours from UTC, and whether the timezone is currently in daylight savings.

Timezones are often identified by three or four letter abbreviations. As can be seen from the list, many of the abbreviations do not uniquely identify a timezone. Furthermore many of the timezones have been altered in the past. The Olson database (or Tz database) by decomposing the world into zones in which the local clocks have all been set to the same time since 1970 and giving these zones unique names.

ruby

The Time class has a zone method which returns the time zone abbreviation for the object. There is a tzinfo gem which can be used to create timezone objects using the Olson database name. This can in turn be used to convert between UTC times and local times which are daylight saving aware.

microseconds

How to get the microseconds component of a combined date and time value. The SI abbreviations for milliseconds and microseconds are ms and μs, respectively. The C standard library uses the letter u as an abbreviation for micro. Here is a struct defined in /usr/include/sys/time.h:

struct timeval {
  time_t       tv_sec;   /* seconds since Jan. 1, 1970 */
  suseconds_t  tv_usec;  /* and microseconds */
};

sleep

How to put the process to sleep for a specified number of seconds. Python and Ruby support sleeping for a fractional number of seconds.

php:

PHP provides usleep which takes an argument in microseconds:

usleep(500000);

perl:

The Perl standard library includes a version of sleep which supports fractional seconds:

use Time::HiRes qw(sleep);

sleep 0.5;

timeout

How to cause a process to timeout if it takes too long.

Container Footnotes

Scripting languages have the same basic container types but the terminology is not universal:

php perl python ruby
array array array, list list, tuple, sequence Array, Enumerable
dictionary array hash dict, mapping Hash

php:

PHP uses the same data structure for arrays and dictionaries.

perl:

array refers to a data type. list refers to a context.

python:

Python has the mutable list and the immutable tuple. Both are sequences. To be a sequence, a class must implement __getitem__, __setitem__, __delitem__, __len__, __contains__, __iter__, __add__, __mul__, __radd__, and __rmul__.

ruby:

Ruby provides an Array datatype. If a class defines an each iterator and a comparison operator <=>, then it can mix in the Enumerable module.

Array Footnotes

literal

Array literal syntax.

perl:

Square brackets create an array and return a reference to it:

$a = [1,2,3]

quote words

The quote words operator, which is a literal for arrays of strings where each string contains a single word.

For languages without this operator, the easiest way to specify such an array of strings is provided.

size

How to get the number of elements in an array.

perl:

The idiomatic way to test whether an array is empty in perl:

if ( not @a ) {
  print "@a is empty\n";
}

python:

The idiomatic way to test whether a list is empty in python:

if not a:
  print "a is empty"

ruby:

The empty list evaluates to true in a condition test. Use the empty? predicate to determine if an array is empty:

if a.empty?
  puts "a is empty"
end

lookup

How to access a value in an array by index.

perl:

A negative index refers to the length - index element.

python:

A negative index refers to the length - index element.

>>> a = [1,2,3]
>>> a[-1]
3

ruby:

A negative index refers to to the length - index element.

update

How to update the value at an index.

out-of-bounds behavior

What happens when the value at an out-of-bounds index is refererenced.

index of array element

perl:

Some techniques for getting the index of an array element.

slice

How to slice a subarray from an array.

perl:

Perl does not directly support slices. Rather Perl arrays can take an array of indices as the index value. As a result the range of values selected can be discontinuous, and the order of the values can be manipulated:

@nums = (1,2,3,4,5,6);                                                                                                                                                  
@nums[(1,3,2,4)];

python:

Slices can leave the first or last index unspecified, in which case the first or last index of the sequence is used:

>>> a=[1,2,3,4,5]
>>> a[:3]
[1, 2, 3]

Python has notation for taking every nth element:

>>> a=[1,2,3,4,5]
>>> a[::2] 
[1, 3, 5]

The third argument in the colon-delimited slice argument can be negative, which reverses the order of the result:

>>> a = [1,2,3,4]
>>> a[::-1]
[4, 3, 2, 1]

ruby:

There is notation for specifying the first index and the number of items in the slice

irb> nums = [1,2,3,4,5]
=> [1, 2, 3, 4, 5]
irb> nums[1,3]
=> [2, 3, 4]

slice to end

How to slice to the end of an array.

manipulate back

How to add and remove elements from the back or high index end of an array.

These operations can be used to use the array as a stack.

manipulate front

How to add and remove elements from the front or low index end of an array.

These operations can be used to use the array as a stack. They can be used with the operations that manipulate the back of the array to use the array as a queue.

concatenate

How to create an array by concatenating two arrays; how to modify an array by concatenating another array to the end of it.

address copy, shallow copy, deep copy

How to make an address copy, a shallow copy, and a deep copy of an array.

After an address copy is made, modifications to the copy also modify the original array.

After a shallow copy is made, the addition, removal, or replacement of elements in the copy does not modify of the original array. However, if elements in the copy are modified, those elements are also modified in the original array.

A deep copy is a recursive copy. The original array is copied and a deep copy is performed on all elements of the array. No change to the contents of the copy will modify the contents of the original array.

perl:

Taking a reference is customary way to make an address copy in Perl, but the Perl example is not equivalent to the other languages because it makes @$b and @a refer to the same array. To make @b and @a refer to the same array, use typeglobs:

*b = *a;

python:

The slice operator can be used to make a shallow copy:

c = a[:]

arrays as function arguments

How arrays are passed as arguments.

iteration

How to iterate through the elements of an array.

perl:

for and foreach are synonyms. Some use for exclusively for C-style for loops and foreach for array iteration.

indexed iteration

How to iterate through the elements of an array while keeping track of the index of each element.

iterate over range

Iterate over a range without instantiating it as a list.

perl:

With Perl 5.005 the for and foreach operators were optimized to not instantiate a range argument as a list.

instantiate range as array

How to convert a range to an array.

sort

How to create a sorted copy of an array, and how to sort an array in place. Also, how to set the comparison function when sorting.

reverse

How to create a reversed copy of an array, and how to reverse an array in place.

python:

reversed returns an iterator which can be used in a for/in construct:

print("counting down:")
for i in reversed([1,2,3]):
  print(i)

reversed can be used to create a reversed list:

a = list(reversed([1,2,3]))

membership

How to test for membership in an array.

intersection

How to compute an intersection.

python:

Python has a set data type which is built-in as of version 2.4. Furthermore, Python has literal syntax for sets: {1,2,3}.

The example computes the intersection by converting the lists to sets. The return value is a set; it can be converted to a list with the list constructor.

ruby:

The intersect operator & always produces an array with no duplicates.

union

python:

The python example computes the union by converting the lists to sets. The return value is a set; it can be converted to a list with the list constructor.

ruby:

The union operator | always produces an array with no duplicates.

map

Create an array by applying an function to each element of a source array.

ruby:

The map! method will apply the function to the elements of the source array in place.

filter

Create an array containing the elements of a source array which match a predicate.

reduce

Return the result of applying a binary operator to all the elements of the array.

perl:

The reduce function was added in Perl 5.10.

universal test

How to test whether a condition holds for all members of an array. Always true for an empty array.

A universal test can be implemented with a filter: filter the set on the negation of the predicate and test whether the result is empty.

existential test

How to test whether an item in an array exists for which a condition holds. Always false for an empty array.

An existential test can be implemented with a filter: filter the set on the predicate and test whether the result is non-empty.

shuffle and sample

How to shuffle an array. How to extract a random sample from an array.

php:

The array_rand function returns a random sample of the indices of an array. The result can easily be converted to a random sample of array values:

$a = array(1, 2, 3, 4);
$sample = array();
foreach (array_rand($a, 2) as $i) { array_push($sample, $a[$i]); }

zip

How to interleave arrays. In the case of two arrays the result is an array of pairs or an associative list.

Dictionary Footnotes

literal

perl:

Curly brackets create a hash and return a reference to it:

$h = { 'hello' => 5, 'goodbye' => 7 }

size

How to get the number of dictionary keys in a dictionary.

lookup

How to lookup a dictionary value using a dictionary key.

perl:

Use the ampersand prefix @ to 'slice' a Perl hash. The index is a list of keys.

%nums = ('b'=>1, 't'=>2, 'a'=>3);
@nums{('b','t')}

out-of-bounds behavior

What happens when a lookup is performed on a key that is not in a dictionary.

is key present

How to check for the presence of a key in a dictionary without raising an exception. Distinguishes from the case where the key is present but mapped to null or a value which evaluates to false.

delete entry

How to remove a key/value pair from a dictionary.

merge

How to merge the values of two dictionaries.

In the examples, if the dictionaries h1 and h2 share keys then the values from h2 will be used in the merged dictionary.

invert

How to turn a dictionary into its inverse. If a key 'foo' is mapped to value 'bar' by a dictionary, then its inverse will map the key 'bar' to the value 'foo'. However, if multiple keys are mapped to the same value in the original dictionary, then some of the keys will be discarded in the inverse.

iteration

How to iterate through the key/value pairs in a dictionary.

python:

If d contains a dictionary then d.items() returns the dictionary as an associative list and d.iteritems() returns an iterator on the dictionary as an associative list.

keys and values as arrays

How to convert the keys of a dictionary to an array; how to convert the values of a dictionary to an array.

default value

How to create a dictionary with a specified default value for missing keys.

perl:

How to use a tied hash. If the CPAN module Tie::ExtraHash is installed there is a shorter way.

Function Footnotes

Python has both functions and methods. Ruby only has methods: functions defined at the top level are in fact methods on a special main object. Perl subroutines can be invoked with a function syntax or a method syntax.

function declaration

How to define a function.

function invocation

How to invoke a function.

python:

When invoking methods and functions, parens are mandatory, even for functions which take no arguments. Omitting the parens returns the function or method as an object. Whitespace can occur between the function name and the following left paren.

Starting with 3.0, print is treated as a function instead of a keyword. Thus parens are mandatory around the print argument.

ruby:

Ruby parens are optional. Leaving out the parens results in ambiguity when function invocations are nested. The interpreter resolves the ambiguity by assigning as many arguments as possible to the innermost function invocation, regardless of its actual arity. As of Ruby 1.9, it is mandatory that the left paren not be separated from the method name by whitespace.

missing argument behavior

How incorrect number of arguments upon invocation are handled.

perl:

Perl collects all arguments into the @_ array, and subroutines normally don't declare the number of arguments they expect. However, this can be done with prototypes. Prototypes also provide a method for taking an array from the caller and giving a reference to the array to the callee.

python:

TypeError is raised if the number of arguments is incorrect.

ruby:

ArgumentError is raised if the number of arguments is incorrect.

default value

How to declare a default value for an argument.

arbitrary number of arguments

How to write a function which accepts a variable number of argument.

php:

It is also possible to use func_num_args and func_get_arg to access the arguments:

for ($i = 1; $i < func_num_args(); $i++) {
    echo func_get_arg($i);
}

named parameters

How to write a function which uses named parameters.

python:

In a function definition, the splat operator * collects the remaining arguments into a list. In a function invocation, the splat can be used to expand an array into separate arguments.

In a function definition the double splat operator ** collects named parameters into a dictionary. In a function invocation, the double splat expands a dictionary into named parameters.

ruby:

pass number or string by reference

perl:

Scalars are passed by reference.

pass array or dictionary by reference

How to pass an array or dictionary without making a copy of it.

perl:

Arrays and hashes are not passed by reference by default. If an array is provided as a argument, each element of the array will be assigned to a parameter. A change to the parameter will change the corresponding value in the original array, but the number of elements in the array cannot be increased. To write a function which changes the size of the array the array must be passed by reference using the backslash notation.

When a hash is provided as a argument each key of the has will be assigned to a parameter and each value of the hash will be assigned to a parameter. In other words the number of parameters seen by the body of the function will be twice the size of the hash. Each value parameter will immediately follow its key parameter.

return value

lambda declaration

How to define a lambda function.

python:

Python lambdas cannot contain newlines or semicolons, and thus are limited to a single statement or expression. Unlike named functions, the value of the last statement or expression is returned, and a return is not necessary or permitted. Lambdas are closures and can refer to local variables in scope, even if they are returned from that scope.

If a closure function is needed that contains more than one statement, use a nested function:

def make_nest(x):
    b = 37
    def nest(y):
        c = x*y
        c *= b
        return c
    return nest

n = make_nest(12*2)
print(n(23))

Python closures are read only.

lambda invocation

function with private state

How to create a function with private state which persists between function invocations.

closure

How to create a first class function with access to the local variables of the local scope in which it was created.

python:

Python has limited closures: access to local variables in the containing scope is read only and the bodies of anonymous functions must consist of a single expression.

generator

How to create a function which can yield a value and suspend execution.

python:

Python generators can be used in for/in statements and list comprehensions.

ruby:

Ruby generators are called fibers. Fibers are coroutines.

Execution Control Footnotes

if

Some optional branching constructs:

perl:

A switch statement was introduced with perl 5.10.

ruby:

case a:
when 0:
  puts "no"
when 1:
  puts "yes"
when 2:
  puts "maybe"
else
  puts "error"
end

while

ruby:

loop creates a loop with no exit condition. until exits when the condition is true.

break/continue/redo

break exits a for or while loop immediately. continue goes to the next iteration of the loop. redo goes back to the beginning of the current iteration.

for

How to write a C-style for loop.

range iteration

How to iterate over a range of integers.

php:

The range operator creates an array in memory. Hence a for loop is more efficient for the given example.

perl:

In a array context such as exists inside the parens of the for construct, the .. operator creates an array in memory. Hence a C-style for loop is more efficient for the given example.

raise exception

How to raise exceptions.

ruby:

Ruby has a throw keyword in addition to raise. throw can have a symbol as an argument, and will not convert a string to a RuntimeError exception.

catch exception

How to catch exceptions.

php:

PHP code must specify a variable name for the caught exception. Exception is the top of the exception hierarchy and will catch all exceptions.

Internal PHP functions usually do not throw exceptions. They can be converted to exceptions with this signal handler:

function exception_error_handler($errno, $errstr, $errfile, $errline ) {
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}
set_error_handler("exception_error_handler");

ruby:

A rescue Exception clause will catch any exception. A rescue clause with no exception type specified will catch exceptions that are subclasses of StandardError. Exceptions outside StandardError are usually unrecoverable and hence not handled in code.

In a rescue clause, the retry keyword will cause the begin clause to be re-executed.

In addition to begin and rescue, ruby has catch:

catch (:done) do
  loop do
    retval = work
    throw :done if retval < 10
  end
end

global variable for last exception raised

The global variable name for the last exception raised.

define exception

How to define a new variable class.

catch exception by type and assign to variable

How to catch exceptions of a specific type and assign the exception a name.

php:

PHP exceptions when caught must always be assigned a variable name.

finally/ensure

Clauses that are guaranteed to be executed even if an exception is thrown or caught.

uncaught exception behavior

System behavior if an exception goes uncaught. Most interpreters print the exception message to stderr and exit with a nonzero status.

start thread

ruby:

Ruby 1.8 threads are green threads, and the interpreter is limited to a single operating system thread.

wait on thread

Environment and I/O Footnotes

external command

When using tclsh as a shell or repl, external commands that do not have the same name as a built-in or user defined function can be executed directly without using the exec command.

backticks

command line args

print to standard out

python:

print appends a newline to the output. To suppress this behavior, put a trailing comma after the last argument. If given multiple arguments, print joins them with spaces.

ruby:

puts appends a newline to the output. print does not.

standard file handles

open file

ruby:

When File.open is given a block, the file is closed when the block terminates.

open file for writing

close file

read line

iterate over a file by line

chomp

Remove a newline, carriage return, or carriage return newline pair from the end of a line if there is one.

php:

chop removes all trailing whitespace. It is an alias for rtrim.

perl:

chomp modifies its argument, which thus must be a scalar, not a string literal.

python:

Python strings are immutable. rstrip returns a modified copy of the string. rstrip('\r\n') is not identical to chomp because it removes all contiguous carriage returns and newlines at the end of the string.

ruby:

chomp! modifies the string in place. chomp returns a modified copy.

read entire file

How to read the contents of a file into memory.

write to file

How to write to a file handle.

flush file

How to flush a file handle that has been written to.

environment variable

exit

python:

It is possible to register code to be executed upon exit:

import atexit
atexit.register(print, "goodbye")

It is possible to terminate a script without executing registered exit code by calling os._exit.

ruby:

It is possible to register code to be executed upon exit:

at_exit { puts "goodbye" }

The script can be terminated without executing registered exit code by calling exit!.

set signal handler

Library and Module Footnotes

How terminology is used in this sheet:

  • library: code in its own file that can be loaded by client code. For interpreted languages, loading a library usually means parsing the library to intermediate representation used by the interpreter VM. It is useless to load an library and not make its definitions available under names in the client code. Hence it is common for languages to import identifiers defined in the library automatically when the library is loaded.
  • module: a set of names that can be imported a unit. Importing a identifier means adding it to a scope. Importing a module means adding all the identifers in the module to a scope.
  • package: a library that can be installed by a package manager.

A few note:

According to our terminology, Perl and Java packages are modules, not packages.

PHP and C++ namespaces are another of example of modules.

We prefer to reserve the term namespace for divisions of the set of names imposed by the parser. For example, the identifier foo in the Perl variables $foo and @foo belong to different namespaces. Another example of namespaces in this sense is the Lisp-1 vs. Lisp-2 distinction: Scheme is a Lisp-1 and has a single namespace, whereas Common Lisp is a Lisp-2 and has multiple namespaces.

Some languages (e.g. Python, Java) impose a one-to-one mapping between libraries and modules. All the definitions for a module must be in a single file, and there are typically restrictions on how the file must be named and where it is located on the filesystem. Other languages allow the definitions for a module to be spread over multiple files or permit a file to contain multiple modules. Ruby and C++ are such languages.

load library

Execute the specified file. Normally this is used on a file which only contains declarations at the top level.

php:

include_once behaves like require_once except that it is not fatal if an error is encountered executing the library.

If it is desirable to reload the library even if it might already have been loaded, use require or include.

perl:

The last expression in a perl library must evaluate to true. When loading a library with use, the suffix of the file must be .pm.

The do directive will re-execute a library even if it has already been loaded.

reload library

How to reload a library. Altered definitions in the library will replace previous versions of the definition.

library path

How to augment the library path by calling a function or manipulating a global variable.

library path environment variable

How to augment the library path by setting an environment variable before invoking the interpreter.

library path command line option

How to augment the library path by providing a command line option when invoking the interpreter.

main in library

How to put code in a library which executes when the file is run as a top-level script and not when the file is loaded as a library.

module declaration

How to declare a section of code as belonging to a module.

submodule declaration

How to declare a section of code as belonging to a submodule.

module separator

The punctuation used to separate the labels in the full name of a submodule.

import module

How to import all the definitions in a module.

import definitions

How to import specific definitions from a module.

managing multiple installations

How to manage multiple versions of the interpreter on the same machine, or the same interpreter with a different set of installed 3rd party packages.

python:

Virtualenv must be downloaded and installed. It is a tarball and it only works on Unix.

list installed packages, install a package

How to show the installed 3rd party packages, and how to install a new 3rd party package.

perl

cpanm is an alternative to cpan which is said to be easier to use.

How to use cpan to install cpanm:

$ sudo cpan -i App::cpanminus

How to install a module with cpanm:

$ sudo cpanm Moose

python

Another way to get the installed modules:

$ python
>>> help('modules')

A Unix specific way to install a Python module that bypasses package management:

$ tar xf libxml2-python-2.6.0.tar.gz
$ cd libxml2-python-2.6.0
$ sudo python setup.py install

Object Footnotes

define class

php:

Properties (i.e. instance variables) must be declared public, protected, or private. Methods can optionally be declared public, protected, or private. Methods without a visibility modifier are public.

perl:

The cheatsheet shows how to create objects using the CPAN module Moose. To the client, a Moose object behaves like a traditional Perl object; it's when a class needs to be defined that Moose code looks different from traditional Perl code.

Moose provides these additional features:

  • shortcuts for creating accessors and delegates
  • attributes can be declared to a be a type
  • classes are objects and can be reflected upon
  • mixins, which are called roles

Moose objects are illustrated instead of Perl objects because Moose is used by the Catalyst web framework, and some of the features in Moose are in the Perl 6 object system. Here is how to define a class in the traditional Perl way:

package Int;

sub new {
  my $class = shift;
  my $v = $_[0] || 0;
  my $self = {value => $v};
  bless $self, $class;
  $self;
}

sub value {
  my $self = shift;
  if ( @_ > 0 ) {
    $self->{'value'} = shift;
  }
  $self->{'value'};
}

sub add {
  my $self = shift;
  $self->value + $_[0];
}

sub DESTROY {
  my $self = shift;
  my $v = $self->value;
  print "bye, $v\n";
}

python:

As of Python 2.2, classes are of two types: new-style classes and old-style classes. The class type is determined by the type of class(es) the class inherits from. If no superclasses are specified, then the class is old-style. As of Python 3.0, all classes are new-style.

New-style classes have these features which old-style classes don't:

  • universal base class called object.
  • descriptors and properties. Also the __getattribute__ method for intercepting all attribute access.
  • change in how the diamond problem is handled. If a class inherits from multiple parents which in turn inherit from a common grandparent, then when checking for an attribute or method, all parents will be checked before the grandparent.

create object

get and set attribute

perl:

Other getters:

$i->value()
$i->{'value'}

Other setters:

$i->{'value'} = $v;

python:

Defining explicit setters and getters in Python is considered poor style. If it becomes necessary to extra logic to attribute, this can be achieved without disrupting the clients of the class by creating a property:

def getValue(self):
  print("getValue called")
  return self.__dict__['value']
def setValue(self,v):
  print("setValue called")
  self.__dict__['value'] = v
value = property(fget=getValue, fset = setValue)

instance variable accessibility

define method

invoke method

perl:

If the method does not take any arguments, the parens are not necessary to invoke the method.

destructor

perl:

Perl destructors are called when the garbage collector reclaims the memory for an object, not when all references to the object go out of scope. In traditional Perl OO, the destructor is named DESTROY, but in Moose OO it is named DEMOLISH.

python:

Python destructors are called when the garbage collector reclaims the memory for an object, not when all references to the object go out of scope.

ruby:

Ruby lacks a destructor. It is possible to register a block to be executed before the memory for an object is released by the garbage collector. A ruby
interpreter may exit without releasing memory for objects that have gone out of scope and in this case the finalizer will not get called. Furthermore, if the finalizer block holds on to a reference to the object, it will prevent the garbage collector from freeing the object.

method missing

php:

Define the method __callStatic to handle calls to undefined class methods.

python:

__getattr__ is invoked when an attribute (instance variable or method) is missing. By contrast, __getattribute__, which is only available in Python 3, is always invoked, and can be used to intercept access to attributes that exist. __setattr__ and __delattr__ are invoked when attempting to set or delete attributes that don't exist. The del statement is used to delete an attribute.

ruby:

Define the method self.method_missing to handle calls to undefined class methods.

inheritance

perl:

Here is how inheritance is handled in traditional Perl OO:

package Counter;

our @ISA = "Int";

my $instances = 0;
our $AUTOLOAD;

sub new {
  my $class = shift;
  my $self = Int->new(@_);
  $instances += 1;
  bless $self, $class;
  $self;
}

sub incr {
  my $self = shift;
  $self->value($self->value + 1);
}
sub instances {
  $instances;
}

sub AUTOLOAD {
  my $self = shift;
  my $argc = scalar(@_);
  print "undefined: $AUTOLOAD " .
    "arity: $argc\n";
}

invoke class method

Reflection Footnotes

class

has method?

perl:

$a->can() returns a reference to the method if it exists, otherwise it returns undef/.

python:

hasattr(o,'reverse') will return True if there is an instance variable named 'reverse'.

message passing

eval

methods

perl:

The following code

$class = ref($a);
keys eval "%${class}::";

gets all symbols defined in the namespace of the class of which $a is an instance. The can method can be used to narrow the list to instance methods.

attributes

perl:

keys %$a assumes the blessed object is a hash reference.

python:

dir(o) returns methods and instance variables.

pretty print

How to display the contents of a data structure for debugging purposes.

source line number and file name

How to get the current line number and file name of the source code.

check syntax

How to check the syntax of code without executing it.

flags for stronger and strongest warnings

Flags to increase the warnings issued by the interpreter:

python:

The -t flag warns about inconsistent use of tabs in the source code. The -3 flag is a Python 2.X option which warns about syntax which is no longer valid in Python 3.X.

Web

http get

url encode/decode

build xml

parse xml

xpath

json

Java Interoperation Footnotes

version

prologue

Code necessary to make java code accessible.

new

How to create a java object.

method

How to invoke a java method.

import

How to import names into the current namespace.

PHP

PHP Manual
General Style and Syntax Codeigniter
Coding Standards Pear
PHP Style Guide Apache

Perl

perldoc
core modules
man perlstyle

The first character of a perl variable ($, @, %) determines the type of value that can be stored in the variable (scalar, array, hash). Using an array variable (@foo) in a scalar context yields the size of the array, and assigning scalar to an array will set the array to contain a single element. $foo[0] accesses the first element of the array @foo, and $bar{‘hello’} accesses the value stored under ‘hello’ in the hash %bar. $#foo is the index of the last element in the array @foo.

Scalars can store a string, integer, or float. If an operator is invoked on a scalar which contains an incorrect data type, perl will always perform an implicit conversion to the correct data type: non-numeric strings evaluate to zero.

Scalars can also contain a reference to a variable, which can be created with a backslash: $baz = \@foo; The original value can be dereferenced with the correct prefix: @$baz. References are how perl creates complex data structures, such as arrays of hashes and arrays of arrays. If $baz contains a reference to an array, then $baz->[0] is the first element of the array. if $baz contains a reference to a hash, $baz->{‘hello’} is the value indexed by ‘hello’.

The literals for arrays and hashes are parens with comma separated elements. Hash literals must contain an even number of elements, and '=>' can be used in placed of a comma ',' between a key and its value. Square brackets, e.g. [ 1, 2, 3 ], create an array and return a reference to it, and curly brackets, e.g. { ‘hello’ => 5, ‘bye’ => 3 }, create a hash and return a reference to it.

By default perl variables are global. They can be made local to the containing block with the my or the local keyword. my gives lexical scope, and local gives dynamic scope. Also by default, the perl interpreter creates a variable whenever it encounters a new variable name in the code. The ‘use strict;’ pragma requires that all variables be declared with my, local, or our. The last is used to declare global variables.

perl functions do not declare their arguments. Any arguments passed to the function are available in the @_ array, and the shift command will operate on this array if no argument is specified. An array passed as an argument is expanded: if the array contains 10 elements, the callee will have 10 arguments in its @_ array. A reference (passing \@foo instead of @foo) can be used to prevent this.

Some of perl’s special variables:

  • $$: pid of the perl process
  • $0: name of the file containing the perl script (may be a full pathname)
  • $@: error message from last eval or require command
  • $&, $`, $’: what last regexp matched, part of the string before and after the match
  • $1..$9: what subpatterns in last regexp matched

Python

2.6
Why Python3 Summary of Backwardly Non-compatible Changes in Python 3
3.1
Jython 2.5.1
Jython Wiki
PEP 8: Style Guide for Python Code van Rossum

Python uses leading whitespace to indicate block structure. It is not recommended to mix tabs and spaces in leading whitespace, but when this is done, a tab is equal to 8 spaces. The command line options '-t' and '-tt' will warn and raise an error respectively when tabs are used inconsistently for indentation.

Regular expressions and functions for interacting with the operating system are not available by default and must be imported to be used, i.e.

import re, sys, os

Identifiers in imported modules must be fully qualified unless imported with from/import:

from sys import path
from re import *

There are two basic sequence types: the mutable list and the immutable tuple. The literal syntax for lists uses square brackets and commas [1,2,3] and the literal syntax for tuples uses parens and commas (1,2,3).

The dictionary data type literal syntax uses curly brackets, colons, and commas { “hello”:5, “goodbye”:7 }. Python 3 adds a literal syntax for sets which uses curly brackets and commas: {1,2,3}. Dictionaries and sets are implemented using hash tables and as a result dictionary keys and set elements must be hashable.

All values that can be stored in a variable and passed to functions as arguments are objects in the sense that they have methods which can be invoked using the method syntax.

Attributes are settable by default. This can be changed by defining a __setattr__ method for the class. The attributes of an object are stored in the __dict__ attribute. Methods must declare the receiver as the first argument.

Classes, methods, functions, and modules are objects. If the body of a class, method, or function definition starts with is a string, it is available available at runtime via __doc__. Code examples in the string which are preceded with '>>>' (the python repl prompt) can be executed by doctest and compared with the output that follows.

Ruby

1.8.7 core
1.9 core
1.8.6 stdlib
Ruby Style Neukirchen
The Unofficial Ruby Usage Guide Macdonald

Ruby consistently treats all values as objects. Classes are objects. Methods, however, are not objects. The system provided classes are open: i.e. the user can add methods to String, Array, or Fixnum. Another difference from python (and perl) is that ruby only permits single inheritance. However, ruby modules are mix-ins and can be used to add methods to a class via the include statement. Ruby methods can be declared private, and this is enforced by the interpreter.

In ruby, there is no difference between named functions and methods: top level ‘functions’ are in fact methods defined on the main object. All methods have a receiver which can be referenced with the self: the receiver does not needed to be treated as an argument like in perl and python.

Ruby has syntax which aids functional programming: a ruby method invocation can be followed by a block, which is a closure. The invoked method can call the block with yield(arg1,…). Also, the invoked method can store the block in a variable if its signature ends with &<varname>. The block can then be invoked with <varname>.call(arg1,…).

History

History of Scripting Languages

Scripting the Operating System

Every program is a "script": a set of instructions for the computer to follow. But early in the evolution of computers a need arose for scripts composed not of just of machine instructions but other programs.

IBM introduced Job Control Language (JCL) with System 360 in 1964. Apparently before JCL IBM machines were run by operators who fed programs through the machine one at a time. JCL provided the ability to run a sequence of jobs as specified on punch cards without manual intervention. The language was rudimentary, not having loops or variable assignment, though it did have parametrized procedures. In the body of a procedure a parameter was preceded by an ampersand: &. The language had conditional logic for taking actions depending upon the return code of a previously executed program. The return code was an integer and zero was used to indicate success.

Also in 1964 Louis Pouzin wrote a program called RUNCOM for the CTSS operating system which could run scripts of CTSS commands. Pouzin thought that shells or command line interpreters should be designed with scriptability in mind and he wrote a paper to that effect.

Unix

The first Unix shell was the one Ken Thomson wrote in 1971. It was scriptable in that it supported if and goto as external commands. It did not have assignment or variables.

In the late 1970s the Unix shell scripting landscape came into place. The Bourne shell replaced the Thomson shell in 7th Edition Unix which shipped in 1979. The Bourne shell dispensed with the goto and instead provided an internally implemented if statement and while and for loops. The Bourne shell had user defined variables which used a dollar sign sigil ($) for access but not assignment.

The C-shell also made its appearance in 1979 with the 2nd Berkeley standard distribution of Unix. It was so named because its control structures resembled the control structures of C. The C-shell eventually acquired a bad reputation as a programming environment. Its true contribution was the introduction of job control and command history. Later shells such as the Korn Shell (1982) and the Bourne Again Shell would attempt to incorporate these features in a manner backwardly comptable with the Bourne shell.

Another landmark in Unix shell scripting was awk which appeared in 1977. awk is a specialized language in that there is an implicit loop and the commands are by default executed on every line of input. However, this was a common pattern in the text file oriented environment of Unix.

more IBM developments

The PC made its appearance in 1981. It came with a command interpreter called COMMAND.COM which could run on a batch file. PC-DOS for that matter was patterned closely on CP/M, the reigning operating system of home computers at the time, which itself borrowed from various DEC operating systems such as TOPS-10. I'm not certain whether CP/M or even TOPS-10 for that matter had batch files. As a programming environment COMMAND.COM was inferior to the Unix shells. Modern Windows systems make this programming environment available with CMD.EXE.

IBM released a scripting language called Rexx for its mainframe operating systems in 1982. Rexx was superior as a programming environment to the Unix shells of the time, and in fact Unix didn't have anything comparable until the appearance of Perl and Tcl in the late 1980s. IBM also released versions of Rexx for OS/2 and PC-DOS.

Perl

In 1987, while he was working for Unisys in Los Angeles, Larry Wall released the first version of a language which would define the scripting language genre. Wall seems to have been both proficient and dissatisfied with Unix shell scripting. Performance was probably one of Wall's complaints, because the interpreter for the new language no longer attempted to resolve unrecognized symbols by trying to run an external command in the search path. Internal functions were provided to do the work of many of the traditional Unix utilities. A side benefit of internal functions is that the special character escaping issues that sometimes plague shell scripting go away.

The performance of arithmetic operations was improved by permitting both strings and numbers to be stored in variables. This caused no inconvenience for the programmer because Perl underlyingly would call atof or sprintf to convert one data type to the other when needed.

Perl introduced two container data types: the array and the hash. As a side note, hashes were not in the original Perl, but they had been introduced by Perl 3.0 in 1989. Variables holding arrays or hashes were identified by the sigils @ and %. With these two types Perl seems to have found the sweet spot. They are a significant reason Perl programming is more pleasant than shell programming, with its anemic arrays that are actually strings of white space separated values. Wall nevertheless saw an advantage in the way shell scripting arrays work: they made it easy to store all the arguments for a command in a single variable. In Perl the same effect was achieved by having arrays automatically expand to separate values when passed to a function.

Perl was both more powerful and easier to use than shell scripting. The easier to use part was achieved through consistency here and there. For example Perl always prefixed scalar variables with dollar signs ($) in contrast to shells which did not used the sigils in assignments. With Perl 2.0 Wall began expanding on the regular expression language. He introduced backslash sequences such as \s and \d for whitespace characters and digits. Since the backslash was the escape character for characters which are special to the regular expression language, Wall adopted the rule that a backslashed punctuation character always matches itself.

the camel book

Wall co-authored a book called Programming Perl for O'Reilly Associates in 1991. On p. xiv the book states Wall's paradoxical "great virtues of a programmer": laziness, impatience, and hubris. On p. 4 we are told that with Perl There's More Than One Way To Do It. As an example of TMTOWTDI p. 5 illustrates three ways of running a Perl program:

$ perl -e 'print "Howdy, world!\n";
Howdy, world!

$ cat howdy
print "Howdy, world!\n";

$ perl howdy
Howdy, world!

$ cat howdy
#!/usr/bin/perl
print "Howdy, world!\n";

$ howdy
Howdy, world!

Perl 5

Scripting the Web

The Original HTTP as defined in 1991
HTML Specification Draft June 1993
WorldWideWeb Browser
Mosaic Web Browser

Tim Berners-Lee created the web in 1990. It ran on a NeXT cube. The browser and the web server communicated via a protocol invented for the purpose called HTTP. The documents were marked up in a type of SGML called HTML. The key innovation was the hyperlink. If the user clicked on a hyperlink, the browser would load the document pointed to by the link. A hyperlink could also take the user to a different section of the current document.

The initial version of HTML included these tags:

html, head, title, body, h1, h2, h3, h4, h5, h6, pre, blockquote, b, i, a, img, ul, ol, li, dl, dt, dd

The browser developed by Berners-Lee was called WorldWideWeb. It was graphical, but it wasn't widely used because it only ran on NeXT. Nicola Pellow wrote a text-only browser and ported it to a variety of platforms in 1991. Mosaic was developed by Andreesen and others at NCSA and released in February 1993. Mosaic was the first browser which could display images in-line with text. It was originally released for X Windows, and it was ported to Macintosh a few months later. Ports for the Amiga and Windows were available in October and December of 1993.

CGI and Forms

RFC 3875: CGI Version 1.1 2004
HTML 2.0 1995
NSAPI Programmer's Guide (pdf) 2000
Apache HTTP Server Project
History of mod_perl
FastCGI Specification 1996

The original web permitted a user to edit a document with a browser, provided he or she had permission to do so. But otherwise the web was static. The group at NCSA developed forms so users could submit data to a web server. They developed the CGI protocol so the server could invoke a separate executable and pass form data to it. The separate executable, referred to as a CGI script in the RFC, could be implemented in almost any language. Perl was a popular early choice. What the CGI script writes to standard out becomes the HTTP response. Usually this would contain a dynamically generated HTML document.

HTML 2.0 introduced the following tags to support forms:

form input select option textarea

The input tag has a type attribute which can be one of the following:

text password checkbox radio image hidden submit reset

If the browser submits the form data with a GET, the form data is included in the URL after a question mark (?). The form data consists of key value pairs. Each key is separated from its value by an equals (=), and the pairs are separated from each other by ampersands (&). The CGI protocol introduces an encoding scheme for escaping the preceding characters in the form data or any other characters that are meaningful or prohibited in URLs. Typically, the web server will set a QUERY_STRING environment variable to pass the GET form data to the CGI script. If the browser submits the data with POST, the form data is encoded in the same manner as for GET, but the data is placed in the HTTP request body. The media type is set to application/x-www-form-urlencoded.

Andreesen and others at NCSA joined the newly founded company Netscape, which released a browser in 1994. Netscape also released a web server with a plug-in architecture. The architecture was an attempt to address the fact that handling web requests with CGI scripts was slow: a separate process was created for each request. With the Netscape web server, the equivalent of a CGI script would be written in C and linked in to the server. The C API that the developer used was called NSAPI. Microsoft developed a similar API called ISAPI for the IIS web server.

The NCSA web server had no such plug-in architecture, but it remained the most popular web server in 1995 even though development had come to a halt. The Apache web server project started up that year; it used the NCSA httpd 1.3 code as a starting point and it was the most popular web server within a year. Apache introduced the Apache API, which permitted C style web development in the manner of NSAPI and ISAPI. The Apache extension mod_perl, released in March 1996, was a client of the Apache API. By means of mod_perl an Apache web server could handle a CGI request in memory using an embedded perl interpreter instead of forking off a separate perl process.

Ousterhout on Scripting Languages

Ousterhout wrote an article for IEEE Computer in 1998 which drew a distinction between system programming languages and scripting languages. As examples of scripting languages Ousterhout cited Perl, Python, Texx, Tcl, Visual Basic, and the Unix shells. To Ousterhout the biggest difference between the two classes of language is that system programming languages are strongly typed whereas scripting languages are typeless. Being typeless was in Ousterhout's mind a necessary trait for a scripting language to serve as "glue language" to connect the components of an application written in other languages. Ousterhout also noted that system programming languages are usually compiled whereas scripting langauges are usually interpreted, and he predicted that the relative use of scripting language would rise.

Postmodern Perl: Python and Ruby

Later Web Developments

HTML Templates

PHP/FI Version 2.0
PHP Usage

Web development with CGI scripts written in Perl was easier than writing web server plug-ins in C. The task of writing Perl CGI scripts was made easier by libraries such as cgi-lib.pl and CGI.pm. These libraries made the query parameters available in a uniform fashion regardless of whether a GET or POST request was being handled and also took care of assembling the headers in the response. Still, CGI scripts tended to be difficult to maintain because of the piecemeal manner in which the response document is assembled.

Rasmus Lerdorf adopted a template approach for maintaining his personal home page. The document to be served up was mostly static HTML with an escaping mechanism for inserting snippets of code. In version 2.0 the escapes were <? code > and <?echo code >. Lerdorf released the code for the original version, called PHP/FI and implemented in Perl, in 1995. The original version was re-implemented in C and version 2.0 was released in 1997. For version 3.0, released in 1998, the name was simplified to PHP. Versions 4.0 and 5.0 were released in 2000 and 2004. PHP greatly increased in popularity with the release of version 4.0. Forum software, blogging software, wikis, and other content management systems (CMS) are often implemented in PHP.

Microsoft added a tempate engine called Active Server Pages (ASP) for IIS in 1996. ASP uses <% code %> and <%= code %> for escapes; the code inside the script could be any number of languages but was usually a dialect of Visual Basic called VBScript. Java Server Pages (JSP), introduced by Sun in 1999, uses the same escapes to embed Java.

MVC Frameworks

The template approach to web development has limitations. Consider the case where the web designer wants to present a certain page if the user is logged in, and a completely unrelated page if the user is not logged in. If the request is routed to an HTML template, then the template will likely have to contain a branch and two mostly unrelated HTML templates. The page that is presented when the user is not logged in might also be displayed under other circumstances, and unless some code sharing mechanism is devised, there will be duplicate code and the maintenance problem that entails.

The solution is for the request to initially be handled by a controller. Based upon the circumstances of the request, the controller chooses the correct HTML template, or view, to present to the user.

Websites frequently retrieve data from and persist data to a database. In a simple PHP website, the SQL might be placed directly in the HTML template. However, this results in a file which mixes three languages: SQL, HTML, and PHP. It is cleaner to put all database access into a separate file or model, and this also promotes code reuse.

The Model-View-Controller design pattern was conceived in 1978. It was used in Smalltalk for GUI design. It was perhaps in Java that the MVC pattern was introduced to web development.

Early versions of Java were more likely to be run in the browser as an applet than in the server. Sun finalized the Servlet API in June 1997. Servlets handled requests and returned responses, and thus were the equivalent of controllers in the MVC pattern. Sun worked on a reference web server which used servlets. This code was donated to the Apache foundation, which used it in the Tomcat webserver, released in 1999. The same year Sun introduced JSP, which corresponds to the view of the MVC pattern.

The Struts MVC framework was introduced in 2000. The Spring MVC framework was introduced in 2002; some prefer it to Struts because it doesn't use Enterprise JavaBeans. Hibernate, introduced in 2002, is an ORM and can serve as the model of an MVC framework.

Ruby on Rails was released in 2004. Ruby has a couple of advantages over Java when implementing an MVC framework. The models can inspect the database and create accessor methods for each column in the underlying table on the fly. Ruby is more concise than Java and has better string manipulation features, so it is a better language to use in HTML templates. Other dynamic languages have built MVC frameworks, e.g. Django for Python.

PHP Version History

1.0 (1995-06-08)

Originally called PHP/FI and implemented in Perl. Reimplemented in C.

2.0 (1997-11-01)

<? code > and <?echo code > are the syntax used to insert code into an HTML template.

3.0 (1998-06-06)

Name simplified to PHP.

4.0 (2000-05-22)

5.0 (2004-07-13)

5.1 (2005-11-24)

5.2 (2006-11-02)

5.3 (2009-06-30)

Namespaces are added.

Perl Version History

Perl 1.0 (gzipped tar) Dec 18, 1987

Perl 2.0 (gizpped tar) Jun 5, 1988

  • New regexp routines derived from Henry Spencer's.
    • Support for /(foo|bar)/.
    • Support for /(foo)*/ and /(foo)+/.
    • \s for whitespace, \S for non-, \d for digit, \D nondigit
  • Local variables in blocks, subroutines and evals.
  • Recursive subroutine calls are now supported.
  • Array values may now be interpolated into lists: unlink 'foo', 'bar', @trashcan, 'tmp';
  • File globbing.
  • Use of <> in array contexts returns the whole file or glob list.
  • New iterator for normal arrays, foreach, that allows both read and write.
  • Ability to open pipe to a forked off script for secure pipes in setuid scripts.
  • File inclusion via do 'foo.pl';
  • More file tests, including -t to see if, for instance, stdin is a terminal. File tests now behave in a more correct manner. You can do file tests on filehandles as well as filenames. The special filetests -T and -B test a file to see if it's text or binary.
  • An eof can now be used on each file of the <> input for such purposes as resetting the line numbers or appending to each file of an inplace edit.
  • Assignments can now function as lvalues, so you can say things like ($HOST = $host) =~ tr/a-z/A-Z/; ($obj = $src) =~ s/\.c$/.o/;
  • You can now do certain file operations with a variable which holds the name of a filehandle, e.g. open(++$incl,$includefilename); $foo = <$incl>;
  • Warnings are now available (with -w) on use of uninitialized variables and on identifiers that are mentioned only once, and on reference to various undefined things.
  • There is now a wait operator.
  • There is now a sort operator.
  • The manual is now not lying when it says that perl is generally faster than sed. I hope.

Perl 3.0 (gzipped tar) Oct 18, 1989)

  • Perl can now handle binary data correctly and has functions to pack and unpack binary structures into arrays or lists. You can now do arbitrary ioctl functions.
  • You can now pass things to subroutines by reference.
  • Debugger enhancements.
  • An array or associative array may now appear in a local() list.
  • Array values may now be interpolated into strings.
  • Subroutine names are now distinguished by prefixing with &. You can call subroutines without using do, and without passing any argument list at all.
  • You can use the new -u switch to cause perl to dump core so that you can run undump and produce a binary executable image. Alternately you can use the "dump" operator after initializing any variables and such.
  • You can now chop lists.
  • Perl now uses /bin/csh to do filename globbing, if available. This means that filenames with spaces or other strangenesses work right.
  • New functions: mkdir and rmdir, getppid, getpgrp and setpgrp, getpriority and setpriority, chroot, ioctl and fcntl, flock, readlink, lstat, rindex, pack and unpack, read, warn, dbmopen and dbmclose, dump, reverse, defined, undef.

Perl 4.0 (gzipped tar) Mar 21, 1991

  • According to wikipedia, this was not a major change. The version was bumped solely because of the publication of the camel book.
  • There were 36 updates numbered 4.0.01 to 4.0.36. These were distributed as patches and usually contained a single commit. The 4.0.36 patch was released in 1993.

Perl 5.0 (Oct 18, 1994)

  • Objects.
  • The documentation is much more extensive and perldoc along with pod is introduced.
  • Lexical scoping available via my. eval can see the current lexical variables.
  • The preferred package delimiter is now :: rather than '.
  • New functions include: abs(), chr(), uc(), ucfirst(), lc(), lcfirst(), chomp(), glob()
  • There is now an English module that provides human readable translations for cryptic variable names.
  • Several previously added features have been subsumed under the new keywords use and no.
  • Pattern matches may now be followed by an m or s modifier to explicitly request multiline or singleline semantics. An s modifier makes . match newline.
  • @ now always interpolates an array in double-quotish strings. Some programs may now need to use backslash to protect any @ that shouldn't interpolate.
  • It is no longer syntactically legal to use whitespace as the name of a variable, or as a delimiter for any kind of quote construct.
  • The -w switch is much more informative.
  • => is now a synonym for comma. This is useful as documentation for arguments that come in pairs, such as initializers for associative arrays, or named arguments to a subroutine.

Perl 5.4 (aka 5.004) (May 1997)

Perl 5.5 (aka 5.005) (July 1998)

  • experimental threads implementation
  • experimental compiler implementation
  • new regular expression constructs: (?<=RE), (?<!RE), (?{ CODE }), (?i-x), (?i:RE), (?(COND)YES_RE|NO_RE), (?>RE), \z

Perl 5.6 Mar 28, 2000

  • Several experimental features, including: support for Unicode, fork() emulation on Windows, 64-bit support, lvalue subroutines, weak references, and new regular expression constructs. See below for the full list.
  • Standard internal representation for strings is UTF-8. (EBCDIC support has been discontinued because of this.)
  • Better support for interpreter concurrency.
  • Lexically scoped warning categories.
  • "our" declarations for global variables.
  • String literals can be written using character ordinals. For example, v102.111.111 is the same as "foo".
  • New syntax for subroutine attributes. (The attrs pragma is now deprecated.)
  • Filehandles can be autovivified. For example: open my $foo, $file or die;
  • open() may be called with three arguments to avoid magic behavior.
  • Support for large files, where available (will be enabled by default.)
  • CHECK blocks. These are like END blocks, but will be called when the compilation of the main program ends.
  • POSIX character class syntax supported, e.g. /[[:alpha:]]/
  • pack() and unpack() support null-terminated strings, native data types, counted strings, and comments in templates
  • Support for binary numbers.
  • exists() and delete() work on array elements. Existence of a subroutine (as opposed to its defined-ness) may also be checked with exists(&sub)).
  • Where possible, Perl does the sane thing to deal with buffered data automatically.
  • binmode() can be used to set :crlf and :raw modes on dosish platforms. The open pragma does the same in the lexical scope, allowing the mode to be set for backticks.
  • Many modules now come standard, including Devel::DProf, Devel::Peek, and Pod::Parser.
  • Many modules have been substantially revised or rewritten.
  • The JPL ("Java Perl Lingo") distribution comes bundled with Perl.
  • Most platform ports have improved functionality. Support for EBCDIC platforms has been withdrawn due to standardization on UTF-8.
  • Much new documentation in the form of tutorials and reference information has been added.
  • Plenty of bug fixes.

Perl 5.8 (July 2002)

  • new threading implementation (5.005 threads are deprecated)
  • better unicode support, including support in regular expressions
  • 64bit support
  • new modules in core library: Digest::MD5, File::Temp, Filter::Simple, libnet, List::Util, Memoize, MIME::Base64, Scalar::Util, Storable, Switch, Test::More, Test::Simple, Text::Balanced, Tie::File

Perl 5.10 (Dec 2007)

  • smart match operator: ~~
  • switch statement
  • named captures in regular expressions
  • recursive regular expressions
  • state variables (like static variables in C functions)
  • defined-or operator: //
  • field hashes for inside-out objects

Perl 5.12 (Apr 2010)

  • Unicode implemented according to Unicode standard
  • improvements to time, fix to Y2038
  • version numbers in package statements

Perl 5.14 (May 2011)

  • /r flag to make s/// non-destructive
  • package Foo {} syntax

Python Version History

Python History Blog by Guido van Rossum
Brief Timeline of Python:
History of Python

0.9 (Feb 20, 1991)

  • classes with inheritance
  • exception handling
  • list, dict, str datatypes
  • modules

1.0 (Jan 26, 1994)

  • lambda, map, filter, reduce

1.1 (Oct 11, 1994)

1.2 (Apr 13, 1995)

1.3 (Oct 13, 1995)

1.4 (Oct 25, 1996)

1.5 (Jan 3, 1998)

  • exceptions are classes, not strings
  • re module (perl style regular expressions) replaces regex
  • nested modules (i.e. hierarchical namespace)

2.0 (Oct 16, 2000)

  • unicode
  • list comprehensions
  • augmented assignment (+=, *=, etc.)
  • cycle detection added to garbage collector

2.1 (Apr 17, 2001)

  • nested lexical scope
  • classes able to override all comparison operators individually

2.2 (Dec 21, 2001)

  • introduction of new-style classes
  • descriptors and properties
  • ability to subclass built-in classes
  • class and static methods
  • callbacks for object property access
  • ability to restrict settable attributes to class defined set
  • base class object added for all built-ins
  • for generalized from sequences to all objects with iter()
  • integers and long integers unified, removing some overflow errors
  • // is integer division, and / is now float division
  • add generators and the yield statement

2.3 (Jul 29, 2003)

  • sets module
  • generators/yield no longer optional
  • source code encodings (for string literals only): # -*- coding: UTF-8 -*-
  • boolean type added

2.4 (Nov 30, 2004)

  • sets built-in
  • Template class for string substitutions (in addition to older % operator)
  • generator expressions (when list comprehensions use too much memory)
  • decorator functions for type checking
  • decimal data type with user specified precision

2.5 (Sep 16, 2006)

  • conditional expressions
  • partial function evaluation: partial()
  • unifed try/except/finally
  • with statement and context management protocol (must be imported from __future__)

2.6 (Oct 1, 2008)

  • -3 command line switch warns about use of features absent in python 3.0
  • with statement does not require import
  • multiprocessing package (processes communicate via queues, threadlike syntax for process management)
  • str.format()
  • as keyword in except clause: except TypeError as exc (old syntax still supported: except TypeError, exc)
  • Abstract Base Classes (ABC): Container, Iterable; user can define an ABC with ABCMeta
  • binary string literal b'', binary and octal numbers 0b01010 and 0o1723
  • class decorators
  • number hierarchy expansion: Number, Fraction, Integral, Complex

3.0 (Dec 3, 2008)

  • old style classes no longer available
  • print is function instead of statement (parens around argument mandatory)
  • comma in except clause discontinued: (except TypeError, exc)
  • 1/2 returns float instead of int (1//2, available since 2.2, returns int)
  • strings (str) are always Unicode; bytes data type available for arbitrary 8-bit data

3.1 (Jun 27, 2009)

  • ordered dictionaries
  • format specifier for thousands separator

2.7 (Jul 3, 2010)

  • adds ordered dictionaries and format specifier for thousands separator from 3.1 to 2.X

3.2 (Feb 20, 2011)

  • argparse added to standard library and intended to replace optparse
  • concurrency.futures module added

Ruby Version History

0.95 (Dec 21, 1995)

1.0 (Dec 25, 1996)

1.4.0 (Aug 13, 1999)

1.6.0 (Sep 19, 2000)

Pickaxe Book (Dec 15, 2001)

1.8.0 (Aug 4, 2003)

1.8.1 (Dec 25, 2003)

Rails (Jul 2004)

1.8.2 (Dec 25, 2004)

1.8.3 (Sep 21, 2005)

1.8.4 (Dec 24, 2005)

1.8.5 (Aug 25, 2006)

1.8.6 (Mar 13, 2007)

1.8.7 (May 31, 2008)

1.9.1 (Jan 31, 2009)

1.9.2 (Aug 24, 2010)

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