Source code for re
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Python/docs/3.8/ modules/re
Source code for re
#
# Secret Labs' Regular Expression Engine
#
# re-compatible interface for the sre matching engine
#
# Copyright (c) 1998-2001 by Secret Labs AB. All rights reserved.
#
# This version of the SRE library can be redistributed under CNRI's
# Python 1.6 license. For any other use, please contact Secret Labs
# AB ([email protected]).
#
# Portions of this engine have been developed in cooperation with
# CNRI. Hewlett-Packard provided funding for 1.6 integration and
# other compatibility work.
#
r"""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) The letters set the corresponding flags defined below.
(?:...) Non-grouping version of regular parentheses.
(?P<name>...) 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 Pattern object.
purge Clear the regular expression cache.
escape Backslash all non-alphanumerics in a string.
Each function other than purge and escape can take an optional 'flags' argument
consisting of one or more of the following module constants, joined by "|".
A, L, and U are mutually exclusive.
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'.
"""
import enum
import sre_compile
import sre_parse
import functools
try:
import _locale
except ImportError:
_locale = None
# public symbols
__all__ = [
"match", "fullmatch", "search", "sub", "subn", "split",
"findall", "finditer", "compile", "purge", "template", "escape",
"error", "Pattern", "Match", "A", "I", "L", "M", "S", "X", "U",
"ASCII", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
"UNICODE",
]
__version__ = "2.2.1"
class RegexFlag(enum.IntFlag):
ASCII = A = sre_compile.SRE_FLAG_ASCII # assume ascii "locale"
IGNORECASE = I = sre_compile.SRE_FLAG_IGNORECASE # ignore case
LOCALE = L = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
UNICODE = U = sre_compile.SRE_FLAG_UNICODE # assume unicode "locale"
MULTILINE = M = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
DOTALL = S = sre_compile.SRE_FLAG_DOTALL # make dot match newline
VERBOSE = X = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
# sre extensions (experimental, don't rely on these)
TEMPLATE = T = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation
def __repr__(self):
if self._name_ is not None:
return f're.{self._name_}'
value = self._value_
members = []
negative = value < 0
if negative:
value = ~value
for m in self.__class__:
if value & m._value_:
value &= ~m._value_
members.append(f're.{m._name_}')
if value:
members.append(hex(value))
res = '|'.join(members)
if negative:
if len(members) > 1:
res = f'~({res})'
else:
res = f'~{res}'
return res
__str__ = object.__str__
globals().update(RegexFlag.__members__)
# sre exception
error = sre_compile.error
# --------------------------------------------------------------------
# public interface
[docs]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."""
return _compile(pattern, flags).match(string)
[docs]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."""
return _compile(pattern, flags).fullmatch(string)
[docs]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."""
return _compile(pattern, flags).search(string)
[docs]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."""
return _compile(pattern, flags).sub(repl, string, count)
[docs]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."""
return _compile(pattern, flags).subn(repl, string, count)
[docs]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."""
return _compile(pattern, flags).split(string, maxsplit)
[docs]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."""
return _compile(pattern, flags).findall(string)
[docs]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."""
return _compile(pattern, flags).finditer(string)
[docs]def compile(pattern, flags=0):
"Compile a regular expression pattern, returning a Pattern object."
return _compile(pattern, flags)
[docs]def purge():
"Clear the regular expression caches"
_cache.clear()
_compile_repl.cache_clear()
def template(pattern, flags=0):
"Compile a template pattern, returning a Pattern object"
return _compile(pattern, flags|T)
# SPECIAL_CHARS
# closing ')', '}' and ']'
# '-' (a range in character set)
# '&', '~', (extended character set operations)
# '#' (comment) and WHITESPACE (ignored) in verbose mode
_special_chars_map = {i: '\\' + chr(i) for i in b'()[]{}?*+-|^$\\.&~# \t\n\r\v\f'}
[docs]def escape(pattern):
"""
Escape special characters in a string.
"""
if isinstance(pattern, str):
return pattern.translate(_special_chars_map)
else:
pattern = str(pattern, 'latin1')
return pattern.translate(_special_chars_map).encode('latin1')
Pattern = type(sre_compile.compile('', 0))
Match = type(sre_compile.compile('', 0).match(''))
# --------------------------------------------------------------------
# internals
_cache = {} # ordered!
_MAXCACHE = 512
def _compile(pattern, flags):
# internal: compile pattern
if isinstance(flags, RegexFlag):
flags = flags.value
try:
return _cache[type(pattern), pattern, flags]
except KeyError:
pass
if isinstance(pattern, Pattern):
if flags:
raise ValueError(
"cannot process flags argument with a compiled pattern")
return pattern
if not sre_compile.isstring(pattern):
raise TypeError("first argument must be string or compiled pattern")
p = sre_compile.compile(pattern, flags)
if not (flags & DEBUG):
if len(_cache) >= _MAXCACHE:
# Drop the oldest item
try:
del _cache[next(iter(_cache))]
except (StopIteration, RuntimeError, KeyError):
pass
_cache[type(pattern), pattern, flags] = p
return p
@functools.lru_cache(_MAXCACHE)
def _compile_repl(repl, pattern):
# internal: compile replacement pattern
return sre_parse.parse_template(repl, pattern)
def _expand(pattern, match, template):
# internal: Match.expand implementation hook
template = sre_parse.parse_template(template, pattern)
return sre_parse.expand_template(template, match)
def _subx(pattern, template):
# internal: Pattern.sub/subn implementation helper
template = _compile_repl(template, pattern)
if not template[0] and len(template[1]) == 1:
# literal replacement
return template[1][0]
def filter(match, template=template):
return sre_parse.expand_template(template, match)
return filter
# register myself for pickling
import copyreg
def _pickle(p):
return _compile, (p.pattern, p.flags)
copyreg.pickle(Pattern, _pickle, _compile)
# --------------------------------------------------------------------
# experimental stuff (see python-dev discussions for details)
class Scanner:
def __init__(self, lexicon, flags=0):
from sre_constants import BRANCH, SUBPATTERN
if isinstance(flags, RegexFlag):
flags = flags.value
self.lexicon = lexicon
# combine phrases into a compound pattern
p = []
s = sre_parse.State()
s.flags = flags
for phrase, action in lexicon:
gid = s.opengroup()
p.append(sre_parse.SubPattern(s, [
(SUBPATTERN, (gid, 0, 0, sre_parse.parse(phrase, flags))),
]))
s.closegroup(gid, p[-1])
p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
self.scanner = sre_compile.compile(p)
def scan(self, string):
result = []
append = result.append
match = self.scanner.scanner(string).match
i = 0
while True:
m = match()
if not m:
break
j = m.end()
if i == j:
break
action = self.lexicon[m.lastindex-1][1]
if callable(action):
self.match = m
action = action(self, m.group())
if action is not None:
append(action)
i = j
return result, string[i:]
