python regex

/ /
                Non-special chars match themselves. Exceptions are special characters:

                \       Escape special char or start a sequence.
                .       Match any char except newline, see re.DOTALL
                ^       Match start of the string, see re.MULTILINE
                $       Match end of the string, see re.MULTILINE
                []      Enclose a set of matchable chars
                R|S     Match either regex R or regex S.
                ()      Create capture group, & indicate precedence

                After '[', enclose a set, the only special chars are:

                ]   End the set, if not the 1st char
                -   A range, eg. a-c matches a, b or c
                ^   Negate the set only if it is the 1st char

                Quantifiers (append '?' for non-greedy):

                {m}     Exactly m repetitions
                {m,n}   From m (default 0) to n (default infinity)
                *       0 or more. Same as {,}
                +       1 or more. Same as {1,}
                ?       0 or 1. Same as {,1}

                Special sequences:

                \A  Start of string
                \b  Match empty string at word (\w+) boundary
                \B  Match empty string not at word boundary
                \d  Digit
                \D  Non-digit
                \s  Whitespace [ \t\n\r\f\v], see LOCALE,UNICODE
                \S  Non-whitespace
                \w  Alphanumeric: [0-9a-zA-Z_], see LOCALE
                \W  Non-alphanumeric
                \Z  End of string
                \g  Match prev named or numbered group,
                        '<' & '>' are literal, e.g. \g<0>
                        or \g<name> (not \g0 or \gname)

                Special character escapes are much like those already escaped in Python string literals.
                Hence regex '\n' is same as regex '\\n':

                \a  ASCII Bell (BEL)
                \f  ASCII Formfeed
                \n  ASCII Linefeed
                \r  ASCII Carriage return
                \t  ASCII Tab
                \v  ASCII Vertical tab
                \\  A single backslash
                \xHH   Two digit hexadecimal character goes here
                \OOO   Three digit octal char (or just use an
                       initial zero, e.g. \0, \09)
                \DD    Decimal number 1 to 99, match
                       previous numbered group

                Extensions. Do not cause grouping, except 'P<name>':

                (?iLmsux)     Match empty string, sets re.X flags
                (?:...)       Non-capturing version of regular parens
                (?P<name>...) Create a named capturing group.
                (?P=name)     Match whatever matched prev named group
                (?#...)       A comment; ignored.
                (?=...)       Lookahead assertion, match without consuming
                (?!...)       Negative lookahead assertion
                (?<=...)      Lookbehind assertion, match if preceded
                (?<!...)      Negative lookbehind assertion
                (?(id)y|n)    Match 'y' if group 'id' matched, else 'n'

                Flags for re.compile(), etc. Combine with '|':

                re.I == re.IGNORECASE   Ignore case
                re.L == re.LOCALE       Make \w, \b, and \s locale dependent
                re.M == re.MULTILINE    Multiline
                re.S == re.DOTALL       Dot matches all (including newline)
                re.U == re.UNICODE      Make \w, \b, \d, and \s unicode dependent
                re.X == re.VERBOSE      Verbose (unescaped whitespace in pattern
                                        is ignored, and '#' marks comment lines)

                Module level functions:

                compile(pattern[, flags]) -> RegexObject
                match(pattern, string[, flags]) -> MatchObject
                search(pattern, string[, flags]) -> MatchObject
                findall(pattern, string[, flags]) -> list of strings
                finditer(pattern, string[, flags]) -> iter of MatchObjects
                split(pattern, string[, maxsplit, flags]) -> list of strings
                sub(pattern, repl, string[, count, flags]) -> string
                subn(pattern, repl, string[, count, flags]) -> (string, int)
                escape(string) -> string
                purge() # the re cache

                RegexObjects (returned from compile()):

                .match(string[, pos, endpos]) -> MatchObject
                .search(string[, pos, endpos]) -> MatchObject
                .findall(string[, pos, endpos]) -> list of strings
                .finditer(string[, pos, endpos]) -> iter of MatchObjects
                .split(string[, maxsplit]) -> list of strings
                .sub(repl, string[, count]) -> string
                .subn(repl, string[, count]) -> (string, int)
                .flags      # int, Passed to compile()
                .groups     # int, Number of capturing groups
                .groupindex # {}, Maps group names to ints
                .pattern    # string, Passed to compile()

                MatchObjects (returned from match() and search()):

                .expand(template) -> string, Backslash & group expansion
                .group([group1...]) -> string or tuple of strings, 1 per arg
                .groups([default]) -> tuple of all groups, non-matching=default
                .groupdict([default]) -> {}, Named groups, non-matching=default
                .start([group]) -> int, Start/end of substring match by group
                .end([group]) -> int, Group defaults to 0, the whole match
                .span([group]) -> tuple (match.start(group), match.end(group))
                .pos       int, Passed to search() or match()
                .endpos    int, "
                .lastindex int, Index of last matched capturing group
                .lastgroup string, Name of last matched capturing group
                .re        regex, As passed to search() or match()
                .string    string, "
taken from tartley