Regular Expressions

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Twelve Metacharacters:

Available in Python

Element	Description
`.`	Any character except newline `\n`
`\d`	Decimal digit, equivalent to `[0-9]`
`\D`	Any non-digit character, equivalent to `[^0-9]`
`\s`	Any whitespace character, equivalent to `[ \t\n\r\f\v]`
`\S`	Any non-whitespace character, equivalent to `[^ \t\n\r\f\v]`
`\w`	Any alphanumeric character, equivalent to `[a-zA-Z0-9_]`
`\W`	Any non-alphanumeric character, equivalent to `[^a-zA-Z0-9_]`

Quantifiers can be applied to characters, character sets, and to groups

Optional (0 or 1 repetition): ?
Zero (0) or more times: *
One (1) or more times: +
Exact repetition and ranges: {}
- Exactly n times: {n}
- Between n and m times (both inclusive): {n,m}
- At least n times: {n,}
- At most n times: {,n}

greedy quantifiers will try to match as much as possible
- default behavior
- biggest possible result
reluctant (non-greedy, lazy) will try to have smalles match possible
- extra ? to quantifier: ??, *? and +?

Identifiers	Match
`^`	Beginning of a line
`$`	End of a line
`\b`	At word boundary
`\B`	Anything that is not word boundary (opposite of `\b`)
`\A`	Beginning of the input
`\Z`	End of the input

RegexObject class in re module
wrapper functions in re module
match tries to match at beginning of string
- pos and slicing can have different results
search is like match in most languages (e.g Perl)
- tries to match at any position in string
Compilation Flags

Used for different purposes:

Add subpatterns that are not in the result (not consuming characters)
- positive: subpattern needs to match
- negative: subpattern must not match
Also called zero-width assertions
Python re module allows look behind only with fixed size (sub-) patterns

	positive	negative
Look ahead	(?=regex)	(?!regex)
Look behind	(?<=regex)	(?<!regex)

General for Python:

import cProfile
cProfile.run("myFunction")