a side-by-side reference sheet

sheet one:version |grammar and execution |variables and expressions |arithmetic and logic |strings |regexes |dates and time |arrays |dictionaries |functions |execution control |exceptions |threads

sheet two:streams |asynchronous events |files |file formats |directories |processes and environment |option parsing |libraries and namespaces |objects |reflection |net and web |databases |unit tests |debugging

sheet two:streams |asynchronous events |files |directories |processes and environment |option parsing |libraries and namespaces |objects |inheritance and polymorphism |reflection |net and web |gui |databases |unit tests |logging |debugging

Version

version used

The versions used for testing code in the reference sheet.

show version

How to get the version.

php:

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

python:

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

import platformplatform.python_version()

ruby:

Also available in the global constantRUBY_VERSION.

implicit prologue

Code which examples in the sheet assume to have already been executed.

#"http://cdnjs.com/libraries/underscore.js">cdnjs hosts underscore.js and other JavaScript libraries for situations where it is inconvenient to have the webserver host the libraries.

When usingunderscore.js with the Node REPL, there is a conflict, since the Node REPL uses the underscore_ variable to store the result of the last evaluation.

$ npm install underscore$ node> var us = require('underscore'); _> us.keys({"one": 1, "two": 2});[ 'one', 'two' ]

php:

Thembstring package adds UTF-8 aware string functions withmb_ prefixes.

python:

We assume thatos,re, andsys are always imported.

Grammar and Execution

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 <?phpphp 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 echophp code ?>.

repl

The customary name of the repl.

php:

Thephp -a REPL does not save or display the result of an expression.

python:

The python repl saves the result of the last statement in_.

ruby:

irb saves the result of the last statement in_.

command line program

How to pass the code to be executed to the interpreter as a command line argument.

block delimiters

How blocks are delimited.

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 encounters 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.

Colons are also used to separate keys from values in dictionary literals and in sequence slice notation.

ruby:

Curly brackets {} delimit blocks. A matched curly bracket pair can be replaced by thedo andend keywords. By convention curly brackets are used for one line blocks.

Theend keyword also terminates blocks started bydef,class, ormodule.

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

statement separator

How the parser determines the end of a statement.

php:

Inside braces statements must be terminated by a semicolon. The following causes a parse error:

<? if (true) { echo "true" } ?>

The last statement inside<?= ?> or<? ?> tags does not need to be semicolon terminated, however. The following code is legal:

<?= $a = 1 ?><? echo $a ?>

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.

source code encoding

How to identify the character encoding for a source code file.

Setting the source code encoding makes it possible to safely use non-ASCII characters in string literals and regular expression literals.

end-of-line comment

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

multiple line comment

How to comment out multiple lines.

python:

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

Variables and Expressions

local variable

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 isNULL.

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 classObject. Assignment toname will create a local variable if one with that name does not exist, even if there is a methodname.

file scope variable

How to define a variable with scope bound by the source file.

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 theglobal keyword. A function must use theglobal keyword to access the global variable.

python:

A variable 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 individually 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 theglobal keyword.

ruby:

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

constant

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.

assignment

How to assign a value to a variable.

python:

If the variable on the left has not previously been defined in the current scope, then it is created. This may hide a variable in a containing scope.

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 (=) when an equality test (==) was intended. Assignments can nevertheless be chained to assign a value to multiple variables:

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 = numsmore_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 will raise aTypeError:

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

In Python 3 the splat operator* can be used to collect the remaining right side elements in a list:

x, y, *z = 1, 2        # assigns [] to zx, y, *z = 1, 2, 3     # assigns [3] to zx, y, *z = 1, 2, 3, 4  # assigns [3, 4] to z

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 previous value of the variable as an argument.

If<OP> is a binary operator and the language has the compound assignment operator<OP>=, then the following are equivalent:

x <OP>= yx = x <OP> y

The compound assignment operators are displayed in this order:

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 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

The C-style increment and decrement operators can be used to increment or decrement values. They return values and thus can be used in expressions. The prefix versions return the value in the variable after mutation, and the postfix version return the value before mutation.

Incrementing a value two or more times in an expression makes the order of evaluation significant:

x = 1;foo(++x, ++x); // foo(2, 3) or foo(3, 2)?x = 1;y = ++x/++x;  // y = 2/3 or y = 3/2?

Python avoids the problem by not having an in-expression increment or decrement.

Ruby mostly avoids the problem by providing a non-mutating increment and decrement. However, here is a Ruby expression which is dependent on order of evaluation:

x = 1y = (x += 1)/(x += 1)

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--;

ruby:

The Integer class definessucc,pred, andnext, which is a synonym forsucc.

The String class definessucc,succ!,next, andnext!.succ! andnext! mutate the string.

null

The null literal.

null test

How to test if a variable contains null.

php:

$v == NULL does not imply that$v isNULL, since any comparison betweenNULL 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"; }

undefined variable

The result of attempting to access an undefined variable.

python:

Because a class can implement aneq method to change the implementation ofv == None, the expression can beTrue whenv is notNone.

php:

PHP does not provide the programmer with a mechanism to distinguish an undefined variable from a variable which has been set to NULL.

A test showing thatisset is the logical negation ofis_null.

python:

How to test if a variable is defined:

not_defined = Falsetry: vexcept NameError:  not_defined = True

ruby:

How to test if a variable is defined:

! defined?(v)

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 asthe ternary operator.

python:

The Python conditional expression comes from Algol.

ruby:

The Rubyif statement is also an expression:

x = if x > 0  xelse  -xend

Arithmetic and Logic

true and false

Literals for the booleans.

These are the return values of the relational operators.

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 testsTRUE == 1 andFALSE == "" evaluate as TRUE but the equality testsTRUE === 1 andFALSE === "" evaluate as FALSE.

falsehoods

Values which behave like the false boolean in a conditional context.

Examples of conditional contexts are the conditional clause of anif statement and the test of awhile loop.

python:

Whether a object evaluates to True or False in a boolean context can be customized by implementing a__nonzero__ (Python 2) or__bool__ (Python 3) instance method for the class.

logical operators

Logical and, or, and not.

php, ruby:

&& and|| have higher precedence than assignment, compound assignment, and the ternary operator (?:), which have higher precedence thanand andor.

relational operators

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

php:

Most of the relational 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.

python:

Relational operators can be chained. The following expressions evaluate to true:

1 < 2 < 31 == 1 != 2

In general ifA_i are expressions andop_i are relational operators, then

    A₁ op₁ A₂ op₂ A₃ … A_n op_n A_n+1

is true if and only if each of the following is true

    A₁ op₁ A₂
    A₂ op₂ A₃
    …
    A_n op_n A_n+1

min and max

How to get the min and max.

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.

divmod

How to get the quotient and remainder with single function call.

integer division by zero

What happens when an integer is divided by zero.

float division

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

float division by zero

What happens when a float is divided by zero.

power

How to get the value of a number raised to a power.

sqrt

The square root function.

sqrt -1

The result of taking the square root of negative one.

transcendental functions

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

python:

Python also hasmath.log10. To compute the log ofx for baseb, use:

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

ruby:

Ruby also hasMath.log2,Math.log10. To compute the log ofx for baseb, use

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

transcendental constants

Constants for π and Euler's constant.

float 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.

absolute value

How to get the absolute value of a number.

integer overflow

What happens when the largest representable integer is exceeded.

float overflow

What happens when the largest representable float is exceeded.

rational numbers

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

ruby:

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

complex numbers

python:

Most of the functions inmath have analogues incmath 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.

set random seed, get and restore seed

How to set the random seed; how to get the current random seed and later restore it.

All the languages in the sheet set the seed automatically to a value that is difficult to predict. The Ruby MRI interpreter uses the current time and process ID, for example. As a result there is usually no need to set the seed.

Setting the seed to a hardcoded value yields a random but repeatable sequence of numbers. This can be used to ensure that unit tests which cover code using random numbers doesn't intermittently fail.

The seed is global state. If multiple functions are generating random numbers then saving and restoring the seed may be necessary to produce a repeatable sequence.

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

radix

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

python

Python has the functionsbin,oct, andhex which take an integer and return a string encoding the integer in base 2, 8, and 16.

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

Strings

string type

The type for a string of Unicode characters.

php:

PHP assumes all strings have single byte characters.

python:

In Python 2.7 thestr type assumes single byte characters. A separateunicode type is available for working with Unicode strings.

In Python 3 thestr type supports multibtye characters and theunicode type has been removed.

There is a mutablebytearray type and an immutablebytes type for working with sequences of bytes.

ruby:

TheString type supports multibtye characters. All strings have an explicitEncoding.

string literal

The syntax for string literals.

python:

String literals may have au prefix

u'lorem ipsum'u"lorem ipsum"u'''loremipsum'''u"""loremipsum"""

In Python 3, these are identical to literals without theu prefix.

In Python 2, these createunicode strings instead ofstr strings. Since the Python 2unicode type corresponds to the Python 3str type, portable code will use theu prefix.

ruby:

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.

s1 = %q(lorem ipsum)s2 = %Q(#{s1} dolor sit amet)

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 istwo lines'''"""This is alsotwo lines"""

literal escapes

Backslash escape sequences for inserting special characters into string literals.

python:

When string literals have anr orR prefix there are no backslash escape sequences and any backslashes thus appear in the created string. The delimiter can be inserted into a string if it is preceded by a backslash, but the backslash is also inserted. It is thus not possible to create a string with anr orR prefix that ends in a backslash. Ther andR prefixes can be used with single or double quotes:

r'C:\Documents and Settings\Admin'r"C:\Windows\System32"

The \uhhhh escapes are also available inside Python 2 Unicode literals. Unicode literals have au prefiix:

u'lambda: \u03bb'

This syntax is also available in Python 3.3, but not Python 3.2. In Python 3.3 it creates a string of typestr which has the same features as theunicode type of Python 2.7.

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.

python:

Triple quotes honor the same backslash escape sequences as regular quotes, so triple quotes can otherwise be used like here documents:

s = '''here documentthere computer'''

ruby:

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

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

variable interpolation

How to interpolate variables into strings.

python:

The f'1 + 1 = {1 + 1}' and f"1 + 1 = {1 + 1}" literals, which support variable interpolation and expression interpolation, are new in Python 3.6.

str.format will take named or positional parameters. When used with named parametersstr.format can mimic the variable interpolation feature of the other languages.

A selection of variables in scope can be passed explicitly:

count = 3item = 'ball'print('{count} {item}s'.format(  count=count,  item=item))

Python 3 hasformat_map which accepts adict as an argument:

count = 3item = 'ball'print('{count} {item}s'.format_map(locals()))

expression interpolation

How to interpolate the result of evaluating an expression into a string.

format string

How to create a string using a printf style format.

python:

The % operator will interpolate arguments into printf-style format strings.

Thestr.format with positional parameters provides an alternative format using curly braces {0}, {1}, … for replacement fields.

The curly braces are escaped by doubling:

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

If the replacement fields appear in sequential order and aren't repeated, the numbers can be omitted:

'lorem {} {} {}'.format('ipsum', 13, 3.7)

are strings mutable?

Are strings mutable?

copy string

How to copy a string such that changes to the original do not modify the copy.

concatenate

The string concatenation operator.

replicate

The string replication operator.

translate case

How to put a string into all caps or all lower case letters.

capitalize

How to capitalize a string and the words in a string.

The examples lowercase non-initial letters.

php:

How to define a UTF-8 aware version ofucfirst. This version also puts the rest of the string in lowercase:

function mb_ucfirst($string, $encoding = "UTF-8"){    $strlen = mb_strlen($string, $encoding);    $firstChar = mb_substr($string, 0, 1, $encoding);    $then = mb_substr(mb_strtolower($string), 1, $strlen - 1, $encoding);    return mb_strtoupper($firstChar, $encoding) . $then;}

ruby:

Rails monkey patches theString class with thetitleize method for capitalizing the words in a string.

trim

How to remove whitespace from the ends of a string.

pad

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

number to string

How to convert numeric data to string data.

format float

How to control the number of digits in a float when converting it to a string.

python:

The number after the decimal controls the number of digits after the decimal:

>>> '%.2f' % math.pi'3.14'

The number after the decimal controls the total number of digits:

>>> '{:.3}'.format(math.pi)'3.14'

string to number

How to convert string data to numeric data.

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.

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.

string join

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

split

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

See alsoscan.

python:

str.split() takes simple strings as delimiters; usere.split() to split on a regular expression:

re.split('\s+', 'do re mi fa')re.split('\s+', 'do re mi fa', 1)

split in two

How to split a string in two.

#"split-keep-delimiters-note">

split and keep delimiters

How to split a string with the delimiters preserved as separate elements.

prefix and suffix test

How to test whether a string begins or ends with a substring.

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; how to find the index of the rightmost occurrence.

extract substring

How to extract a substring from a string by index.

byte array type

The type for an array of bytes.

byte array to string

How to convert an array of bytes to a string of Unicode characters.

string to byte array

How to convert a string of Unicode characters to an array of bytes.

character lookup

How to look up the character in a string at an 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.

to array of characters

How to split a string into an array of single character strings.

translate characters

How to apply a character mapping to a string.

python:

In Python 2, the string of lowercase letters is instring.lowercase instead ofstring.ascii_lowercase.

In Python 2, themaketrans function is in the modulestring instead ofstr.

delete characters

How to remove all specified characters from a string; how to remove all but the specified characters from a string.

squeeze characters

How to replace multiple adjacent occurrences of a character with a single occurrence.

Regular Expressions

• PHP PCRE Regexes
• Python re library:2.7,3.1
• Ruby Regexp

Regular expressions or regexes are a way of specifying sets of strings. If a string belongs to the set, the string and regex "match". Regexes can also be used to parse strings.

The modern notation for regexes was introduced by Unix command line tools in the 1970s. POSIX standardized the notation into two types: extended regexes and the more archaic basic regexes. Perl regexes are extended regexes augmented by new character class abbreviations and a few other features introduced by the Perl interpreter in the 1990s. All the languages in this sheet use Perl regexes.

Any string that doesn't contain regex metacharacters is a regex which matches itself. The regex metacharacters are:[ ] . | ( ) * + ? { } ^ $ \

character classes: [ ] .

A character class is a set of characters in brackets:[ ]. When used in a regex it matches any character it contains.

Character classes have their own set of metacharacters:^ - \ ]

The^ is only special when it is the first character in the character class. Such a character class matches its complement; that is, any character not inside the brackets. When not the first character the^ refers to itself.

The hyphen is used to specify character ranges: e.g.0-9 orA-Z. When the hyphen is first or last inside the brackets it matches itself.

The backslash can be used to escape the above characters or the terminal character class delimiter:]. It can be used in character class abbreviations or string backslash escapes.

The period. is a character class abbreviation which matches any character except for newline. In all languages the period can be made to match all characters. PHP uses them modifier. Python uses there.M flag. Ruby uses thes modifier.

character class abbreviations:

alternation and grouping: | ( )

The vertical pipe | is used for alternation and parens () for grouping.

A vertical pipe takes as its arguments everything up to the next vertical pipe, enclosing paren, or end of string.

Parentheses control the scope of alternation and the quantifiers described below. They are also used for capturing groups, which are the substrings which matched parenthesized parts of the regular expression. Each language numbers the groups and provides a mechanism for extracting them when a match is made. A parenthesized subexpression can be removed from the groups with this syntax:(?:expr)

quantifiers: * + ? { }

As an argument quantifiers take the preceding regular character, character class, or group. The argument can itself be quantified, so that^a{4}*$ matches strings with the letter a in multiples of 4.

When there is a choice, greedy quantifiers will match the maximum possible number of occurrences of the argument. Lazy quantifiers match the minimum possible number.

anchors: ^ $

escaping: \

To match a metacharacter, put a backslash in front of it. To match a backslash use two backslashes.

php:

PHP 5.3 still supports the EREG engine, though the functions which use it are deprecated. These include thesplit function and functions which start withereg. The preferred functions arepreg_split and the other functions with apreg prefix.

literal, custom delimited literal

The literal for a regular expression; the literal for a regular expression with a custom delimiter.

#"ascii-char-class-abbrev-note">

ascii character class abbreviations

The supportedcharacter class abbreviations.

Note that\h refers to horizontal whitespace (i.e. a space or tab) in PHP and a hex digit in Ruby. Similarly\H refers to something that isn't horizontal whitespace in PHP and isn't a hex digit in Ruby.

unicode character class abbreviations

The supported character class abbreviations for sets of Unicode characters.

Each Unicode character belongs to one of these major categories:

Each major category is subdivided into multiple minor categories. Each minor category has a two letter code, where the first letter is the major category. For example,Nd is "Number, decimal digit".

DownloadUnicodeData.txt to find out which major and minor category and character belongs to.

anchors

The supported anchors.

match test

How to test whether a string matches a regular expression.

python:

There.match function returns true only if the regular expression matches the beginning of the string.re.search returns true if the regular expression matches any substring of the of string.

ruby:

match is a method of bothRegexp andString so can match with both

/1999/.match("1999")

and

"1999".match(/1999/)

When variables are involved it is safer to invoke theRegexp method because string variables are more likely to containnil.

case insensitive match test

How to perform a case insensitive match test.

modifiers

Modifiers that can be used to adjust the behavior of a regular expression.

The lists are not comprehensive. For all languages except Ruby there are additional modifiers.

$s = "foo bar bar";preg_replace('/bar/', "baz", $s, 1);

s = 'foo bar bar're.compile('bar').sub('baz', s, 1)

"1999-07-08"[/(\d{4})-(\d{2})-(\d{2})/, 1]

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 */};

import timeutc = time.gmtime(time.time())t = time.localtime(time.time())

import calendarimport datetimeint(datetime.datetime.now().strftime('%s'))calendar.timegm(datetime.datetime.utcnow().utctimetuple())

$ zdump /etc/localtime/etc/localtime  Tue Dec 30 10:03:27 2014 PST

date.timezone = "America/Los_Angeles"

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

usleep(500000);

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

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