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/Lib/re.py

http://unladen-swallow.googlecode.com/
Python | 327 lines | 306 code | 4 blank | 17 comment | 2 complexity | ac9b579d9047c26e7e4ce925854ff1e8 MD5 | raw file
  1#
  2# Secret Labs' Regular Expression Engine
  3#
  4# re-compatible interface for the sre matching engine
  5#
  6# Copyright (c) 1998-2001 by Secret Labs AB.  All rights reserved.
  7#
  8# This version of the SRE library can be redistributed under CNRI's
  9# Python 1.6 license.  For any other use, please contact Secret Labs
 10# AB (info@pythonware.com).
 11#
 12# Portions of this engine have been developed in cooperation with
 13# CNRI.  Hewlett-Packard provided funding for 1.6 integration and
 14# other compatibility work.
 15#
 16
 17r"""Support for regular expressions (RE).
 18
 19This module provides regular expression matching operations similar to
 20those found in Perl.  It supports both 8-bit and Unicode strings; both
 21the pattern and the strings being processed can contain null bytes and
 22characters outside the US ASCII range.
 23
 24Regular expressions can contain both special and ordinary characters.
 25Most ordinary characters, like "A", "a", or "0", are the simplest
 26regular expressions; they simply match themselves.  You can
 27concatenate ordinary characters, so last matches the string 'last'.
 28
 29The special characters are:
 30    "."      Matches any character except a newline.
 31    "^"      Matches the start of the string.
 32    "$"      Matches the end of the string or just before the newline at
 33             the end of the string.
 34    "*"      Matches 0 or more (greedy) repetitions of the preceding RE.
 35             Greedy means that it will match as many repetitions as possible.
 36    "+"      Matches 1 or more (greedy) repetitions of the preceding RE.
 37    "?"      Matches 0 or 1 (greedy) of the preceding RE.
 38    *?,+?,?? Non-greedy versions of the previous three special characters.
 39    {m,n}    Matches from m to n repetitions of the preceding RE.
 40    {m,n}?   Non-greedy version of the above.
 41    "\\"     Either escapes special characters or signals a special sequence.
 42    []       Indicates a set of characters.
 43             A "^" as the first character indicates a complementing set.
 44    "|"      A|B, creates an RE that will match either A or B.
 45    (...)    Matches the RE inside the parentheses.
 46             The contents can be retrieved or matched later in the string.
 47    (?iLmsux) Set the I, L, M, S, U, or X flag for the RE (see below).
 48    (?:...)  Non-grouping version of regular parentheses.
 49    (?P<name>...) The substring matched by the group is accessible by name.
 50    (?P=name)     Matches the text matched earlier by the group named name.
 51    (?#...)  A comment; ignored.
 52    (?=...)  Matches if ... matches next, but doesn't consume the string.
 53    (?!...)  Matches if ... doesn't match next.
 54    (?<=...) Matches if preceded by ... (must be fixed length).
 55    (?<!...) Matches if not preceded by ... (must be fixed length).
 56    (?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
 57                       the (optional) no pattern otherwise.
 58
 59The special sequences consist of "\\" and a character from the list
 60below.  If the ordinary character is not on the list, then the
 61resulting RE will match the second character.
 62    \number  Matches the contents of the group of the same number.
 63    \A       Matches only at the start of the string.
 64    \Z       Matches only at the end of the string.
 65    \b       Matches the empty string, but only at the start or end of a word.
 66    \B       Matches the empty string, but not at the start or end of a word.
 67    \d       Matches any decimal digit; equivalent to the set [0-9].
 68    \D       Matches any non-digit character; equivalent to the set [^0-9].
 69    \s       Matches any whitespace character; equivalent to [ \t\n\r\f\v].
 70    \S       Matches any non-whitespace character; equiv. to [^ \t\n\r\f\v].
 71    \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_].
 72             With LOCALE, it will match the set [0-9_] plus characters defined
 73             as letters for the current locale.
 74    \W       Matches the complement of \w.
 75    \\       Matches a literal backslash.
 76
 77This module exports the following functions:
 78    match    Match a regular expression pattern to the beginning of a string.
 79    search   Search a string for the presence of a pattern.
 80    sub      Substitute occurrences of a pattern found in a string.
 81    subn     Same as sub, but also return the number of substitutions made.
 82    split    Split a string by the occurrences of a pattern.
 83    findall  Find all occurrences of a pattern in a string.
 84    finditer Return an iterator yielding a match object for each match.
 85    compile  Compile a pattern into a RegexObject.
 86    purge    Clear the regular expression cache.
 87    escape   Backslash all non-alphanumerics in a string.
 88
 89Some of the functions in this module takes flags as optional parameters:
 90    I  IGNORECASE  Perform case-insensitive matching.
 91    L  LOCALE      Make \w, \W, \b, \B, dependent on the current locale.
 92    M  MULTILINE   "^" matches the beginning of lines (after a newline)
 93                   as well as the string.
 94                   "$" matches the end of lines (before a newline) as well
 95                   as the end of the string.
 96    S  DOTALL      "." matches any character at all, including the newline.
 97    X  VERBOSE     Ignore whitespace and comments for nicer looking RE's.
 98    U  UNICODE     Make \w, \W, \b, \B, dependent on the Unicode locale.
 99
100This module also defines an exception 'error'.
101
102"""
103
104import sys
105import sre_compile
106import sre_parse
107
108# public symbols
109__all__ = [ "match", "search", "sub", "subn", "split", "findall",
110    "compile", "purge", "template", "escape", "I", "L", "M", "S", "X",
111    "U", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
112    "UNICODE", "error" ]
113
114__version__ = "2.2.1"
115
116# flags
117I = IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
118L = LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
119U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode locale
120M = MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
121S = DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
122X = VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
123
124# sre extensions (experimental, don't rely on these)
125T = TEMPLATE = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
126DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation
127
128# sre exception
129error = sre_compile.error
130
131# --------------------------------------------------------------------
132# public interface
133
134def match(pattern, string, flags=0):
135    """Try to apply the pattern at the start of the string, returning
136    a match object, or None if no match was found."""
137    return _compile(pattern, flags).match(string)
138
139def search(pattern, string, flags=0):
140    """Scan through string looking for a match to the pattern, returning
141    a match object, or None if no match was found."""
142    return _compile(pattern, flags).search(string)
143
144def sub(pattern, repl, string, count=0):
145    """Return the string obtained by replacing the leftmost
146    non-overlapping occurrences of the pattern in string by the
147    replacement repl.  repl can be either a string or a callable;
148    if a string, backslash escapes in it are processed.  If it is
149    a callable, it's passed the match object and must return
150    a replacement string to be used."""
151    return _compile(pattern, 0).sub(repl, string, count)
152
153def subn(pattern, repl, string, count=0):
154    """Return a 2-tuple containing (new_string, number).
155    new_string is the string obtained by replacing the leftmost
156    non-overlapping occurrences of the pattern in the source
157    string by the replacement repl.  number is the number of
158    substitutions that were made. repl can be either a string or a
159    callable; if a string, backslash escapes in it are processed.
160    If it is a callable, it's passed the match object and must
161    return a replacement string to be used."""
162    return _compile(pattern, 0).subn(repl, string, count)
163
164def split(pattern, string, maxsplit=0):
165    """Split the source string by the occurrences of the pattern,
166    returning a list containing the resulting substrings."""
167    return _compile(pattern, 0).split(string, maxsplit)
168
169def findall(pattern, string, flags=0):
170    """Return a list of all non-overlapping matches in the string.
171
172    If one or more groups are present in the pattern, return a
173    list of groups; this will be a list of tuples if the pattern
174    has more than one group.
175
176    Empty matches are included in the result."""
177    return _compile(pattern, flags).findall(string)
178
179if sys.hexversion >= 0x02020000:
180    __all__.append("finditer")
181    def finditer(pattern, string, flags=0):
182        """Return an iterator over all non-overlapping matches in the
183        string.  For each match, the iterator returns a match object.
184
185        Empty matches are included in the result."""
186        return _compile(pattern, flags).finditer(string)
187
188def compile(pattern, flags=0):
189    "Compile a regular expression pattern, returning a pattern object."
190    return _compile(pattern, flags)
191
192def purge():
193    "Clear the regular expression cache"
194    _cache.clear()
195    _cache_repl.clear()
196
197def template(pattern, flags=0):
198    "Compile a template pattern, returning a pattern object"
199    return _compile(pattern, flags|T)
200
201_alphanum = {}
202for c in 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890':
203    _alphanum[c] = 1
204del c
205
206def escape(pattern):
207    "Escape all non-alphanumeric characters in pattern."
208    s = list(pattern)
209    alphanum = _alphanum
210    for i in range(len(pattern)):
211        c = pattern[i]
212        if c not in alphanum:
213            if c == "\000":
214                s[i] = "\\000"
215            else:
216                s[i] = "\\" + c
217    return pattern[:0].join(s)
218
219# --------------------------------------------------------------------
220# internals
221
222_cache = {}
223_cache_repl = {}
224
225_pattern_type = type(sre_compile.compile("", 0))
226
227_MAXCACHE = 100
228
229def _compile(*key):
230    # internal: compile pattern
231    cachekey = (type(key[0]),) + key
232    p = _cache.get(cachekey)
233    if p is not None:
234        return p
235    pattern, flags = key
236    if isinstance(pattern, _pattern_type):
237        if flags:
238            raise ValueError('Cannot process flags argument with a compiled pattern')
239        return pattern
240    if not sre_compile.isstring(pattern):
241        raise TypeError, "first argument must be string or compiled pattern"
242    try:
243        p = sre_compile.compile(pattern, flags)
244    except error, v:
245        raise error, v # invalid expression
246    if len(_cache) >= _MAXCACHE:
247        _cache.clear()
248    _cache[cachekey] = p
249    return p
250
251def _compile_repl(*key):
252    # internal: compile replacement pattern
253    p = _cache_repl.get(key)
254    if p is not None:
255        return p
256    repl, pattern = key
257    try:
258        p = sre_parse.parse_template(repl, pattern)
259    except error, v:
260        raise error, v # invalid expression
261    if len(_cache_repl) >= _MAXCACHE:
262        _cache_repl.clear()
263    _cache_repl[key] = p
264    return p
265
266def _expand(pattern, match, template):
267    # internal: match.expand implementation hook
268    template = sre_parse.parse_template(template, pattern)
269    return sre_parse.expand_template(template, match)
270
271def _subx(pattern, template):
272    # internal: pattern.sub/subn implementation helper
273    template = _compile_repl(template, pattern)
274    if not template[0] and len(template[1]) == 1:
275        # literal replacement
276        return template[1][0]
277    def filter(match, template=template):
278        return sre_parse.expand_template(template, match)
279    return filter
280
281# register myself for pickling
282
283import copy_reg
284
285def _pickle(p):
286    return _compile, (p.pattern, p.flags)
287
288copy_reg.pickle(_pattern_type, _pickle, _compile)
289
290# --------------------------------------------------------------------
291# experimental stuff (see python-dev discussions for details)
292
293class Scanner:
294    def __init__(self, lexicon, flags=0):
295        from sre_constants import BRANCH, SUBPATTERN
296        self.lexicon = lexicon
297        # combine phrases into a compound pattern
298        p = []
299        s = sre_parse.Pattern()
300        s.flags = flags
301        for phrase, action in lexicon:
302            p.append(sre_parse.SubPattern(s, [
303                (SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
304                ]))
305        s.groups = len(p)+1
306        p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
307        self.scanner = sre_compile.compile(p)
308    def scan(self, string):
309        result = []
310        append = result.append
311        match = self.scanner.scanner(string).match
312        i = 0
313        while 1:
314            m = match()
315            if not m:
316                break
317            j = m.end()
318            if i == j:
319                break
320            action = self.lexicon[m.lastindex-1][1]
321            if hasattr(action, '__call__'):
322                self.match = m
323                action = action(self, m.group())
324            if action is not None:
325                append(action)
326            i = j
327        return result, string[i:]