# Python Regex Cheatsheet

- Regular Expression Basics:

    .           Any character except newline
    a           The character a
    ab          The string ab
    a|b         a or b
    a*          0 or more a's
    \           Escapes a special character

- Regular Expression Quantifiers:

    *           0 or more
    +           1 or more
    ?           0 or 1
    {2}         Exactly 2
    {2, 5}      Between 2 and 5
    {2,}        2 or more
    (,5}        Up to 5

    Default is greedy. Append ? for reluctant.

- Regular Expression Groups:

    (...)       Capturing group
    (?P<Y>...)  Capturing group named Y
    (?:...)     Non-capturing group
    \Y          Match the Y'th captured group
    (?P=Y)      Match the named group Y
    (?#...)     Comment

- Regular Expression Character Classes:

    [ab-d]      One character of: a, b, c, d
    [^ab-d]     One character except: a, b, c, d
    [\b]        Backspace character
    \d          One digit
    \D          One non-digit
    \s          One whitespace
    \S          One non-whitespace
    \w          One word character
    \W          One non-word character

- Regular Expression Assertions:

    ^           Start of string
    \A          Start of string, ignores m flag
    $           End of string
    \Z          End of string, ignores m flag
    \b          Word boundary
    \B          Non-word boundary
    (?=...)     Positive lookahead
    (?!...)     Negative lookahead
    (?<=...)    Positive lookbehind
    (?<!...)    Negative lookbehind
    (?()|)      Conditional

- Regular Expression Flags:

    i           Ignore case
    m           ^ and $ match start and end of line
    s           . matches newline as well
    x           Allow spaces and comments
    L           Locale character classes
    u           Unicode character classes
    (?iLmsux)   Set flags within regex

- Regular Expression Special Characters:

    \n          Newline
    \r          Carriage return
    \t          Tab
    \YYY        Octal character YYY
    \xYY        Hexadecimal character YY

- Regular Expression Replacement:

    \g<0>       Insert entire match
    \g<Y>       Insert match Y (name or number)
    \Y          Insert group numbered Y