Python Regular Expressions Module: re

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re module

Support for regular expressions (RE).

This module provides regular expression matching operations similar to those found in Perl. It supports both 8-bit and Unicode strings; both the pattern and the strings being processed can contain null bytes and characters outside the US ASCII range.

Regular expressions can contain both special and ordinary characters. Most ordinary characters, like "A", "a", or "0", are the simplest regular expressions; they simply match themselves. You can concatenate ordinary characters, so last matches the string 'last'.

The special characters are: "." Matches any character except a newline. "^" Matches the start of the string. "$" Matches the end of the string or just before the newline at the end of the string. "" Matches 0 or more (greedy) repetitions of the preceding RE. Greedy means that it will match as many repetitions as possible. "+" Matches 1 or more (greedy) repetitions of the preceding RE. "?" Matches 0 or 1 (greedy) of the preceding RE. ?,+?,?? Non-greedy versions of the previous three special characters. {m,n} Matches from m to n repetitions of the preceding RE. {m,n}? Non-greedy version of the above. "\" Either escapes special characters or signals a special sequence. [] Indicates a set of characters. A "^" as the first character indicates a complementing set. "|" A|B, creates an RE that will match either A or B. (...) Matches the RE inside the parentheses. The contents can be retrieved or matched later in the string. (?aiLmsux) Set the A, I, L, M, S, U, or X flag for the RE (see below). (?:...) Non-grouping version of regular parentheses. (?P...) The substring matched by the group is accessible by name. (?P=name) Matches the text matched earlier by the group named name. (?#...) A comment; ignored. (?=...) Matches if ... matches next, but doesn't consume the string. (?!...) Matches if ... doesn't match next. (?<=...) Matches if preceded by ... (must be fixed length). (?<!...) Matches if not preceded by ... (must be fixed length). (?(id/name)yes|no) Matches yes pattern if the group with id/name matched, the (optional) no pattern otherwise.

The special sequences consist of "\" and a character from the list below. If the ordinary character is not on the list, then the resulting RE will match the second character. \number Matches the contents of the group of the same number. \A Matches only at the start of the string. \Z Matches only at the end of the string. \b Matches the empty string, but only at the start or end of a word. \B Matches the empty string, but not at the start or end of a word. \d Matches any decimal digit; equivalent to the set [0-9] in bytes patterns or string patterns with the ASCII flag. In string patterns without the ASCII flag, it will match the whole range of Unicode digits. \D Matches any non-digit character; equivalent to [^\d]. \s Matches any whitespace character; equivalent to [ \t\n\r\f\v] in bytes patterns or string patterns with the ASCII flag. In string patterns without the ASCII flag, it will match the whole range of Unicode whitespace characters. \S Matches any non-whitespace character; equivalent to [^\s]. \w Matches any alphanumeric character; equivalent to [a-zA-Z0-9_] in bytes patterns or string patterns with the ASCII flag. In string patterns without the ASCII flag, it will match the range of Unicode alphanumeric characters (letters plus digits plus underscore). With LOCALE, it will match the set [0-9_] plus characters defined as letters for the current locale. \W Matches the complement of \w. \ Matches a literal backslash.

This module exports the following functions: match Match a regular expression pattern to the beginning of a string. fullmatch Match a regular expression pattern to all of a string. search Search a string for the presence of a pattern. sub Substitute occurrences of a pattern found in a string. subn Same as sub, but also return the number of substitutions made. split Split a string by the occurrences of a pattern. findall Find all occurrences of a pattern in a string. finditer Return an iterator yielding a match object for each match. compile Compile a pattern into a RegexObject. purge Clear the regular expression cache. escape Backslash all non-alphanumerics in a string.

Some of the functions in this module takes flags as optional parameters: A ASCII For string patterns, make \w, \W, \b, \B, \d, \D match the corresponding ASCII character categories (rather than the whole Unicode categories, which is the default). For bytes patterns, this flag is the only available behaviour and needn't be specified. I IGNORECASE Perform case-insensitive matching. L LOCALE Make \w, \W, \b, \B, dependent on the current locale. M MULTILINE "^" matches the beginning of lines (after a newline) as well as the string. "$" matches the end of lines (before a newline) as well as the end of the string. S DOTALL "." matches any character at all, including the newline. X VERBOSE Ignore whitespace and comments for nicer looking RE's. U UNICODE For compatibility only. Ignored for string patterns (it is the default), and forbidden for bytes patterns.

This module also defines an exception 'error'.

Module variables

var A

var ASCII

var DOTALL

var I

var IGNORECASE

var L

var LOCALE

var M

var MULTILINE

var S

var U

var UNICODE

var VERBOSE

var X

Functions

def compile(

pattern, flags=0)

Compile a regular expression pattern, returning a pattern object.

def escape(

pattern)

Escape all the characters in pattern except ASCII letters, numbers and '_'.

def findall(

pattern, string, flags=0)

Return a list of all non-overlapping matches in the string.

If one or more capturing groups are present in the pattern, return a list of groups; this will be a list of tuples if the pattern has more than one group.

Empty matches are included in the result.

def finditer(

pattern, string, flags=0)

Return an iterator over all non-overlapping matches in the string. For each match, the iterator returns a match object.

Empty matches are included in the result.

def fullmatch(

pattern, string, flags=0)

Try to apply the pattern to all of the string, returning a match object, or None if no match was found.

def match(

pattern, string, flags=0)

Try to apply the pattern at the start of the string, returning a match object, or None if no match was found.

def purge(

)

Clear the regular expression caches

def search(

pattern, string, flags=0)

Scan through string looking for a match to the pattern, returning a match object, or None if no match was found.

def split(

pattern, string, maxsplit=0, flags=0)

Split the source string by the occurrences of the pattern, returning a list containing the resulting substrings. If capturing parentheses are used in pattern, then the text of all groups in the pattern are also returned as part of the resulting list. If maxsplit is nonzero, at most maxsplit splits occur, and the remainder of the string is returned as the final element of the list.

def sub(

pattern, repl, string, count=0, flags=0)

Return the string obtained by replacing the leftmost non-overlapping occurrences of the pattern in string by the replacement repl. repl can be either a string or a callable; if a string, backslash escapes in it are processed. If it is a callable, it's passed the match object and must return a replacement string to be used.

def subn(

pattern, repl, string, count=0, flags=0)

Return a 2-tuple containing (new_string, number). new_string is the string obtained by replacing the leftmost non-overlapping occurrences of the pattern in the source string by the replacement repl. number is the number of substitutions that were made. repl can be either a string or a callable; if a string, backslash escapes in it are processed. If it is a callable, it's passed the match object and must return a replacement string to be used.

def template(

pattern, flags=0)

Compile a template pattern, returning a pattern object

Classes

class error

Exception raised for invalid regular expressions.

Attributes:

msg: The unformatted error message
pattern: The regular expression pattern
pos: The index in the pattern where compilation failed (may be None)
lineno: The line corresponding to pos (may be None)
colno: The column corresponding to pos (may be None)

Ancestors (in MRO)

  • error
  • builtins.Exception
  • builtins.BaseException
  • builtins.object

Class variables

var args

Static methods

def __init__(

self, msg, pattern=None, pos=None)

Initialize self. See help(type(self)) for accurate signature.

Instance variables

var msg

var pattern

var pos