Lib/re.py

   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
  17 r"""Support for regular expressions (RE).
  18
  19 This module provides regular expression matching operations similar to
  20 those found in Perl.  It supports both 8-bit and Unicode strings; both
  21 the pattern and the strings being processed can contain null bytes and
  22 characters outside the US ASCII range.
  23
  24 Regular expressions can contain both special and ordinary characters.
  25 Most ordinary characters, like "A", "a", or "0", are the simplest
  26 regular expressions; they simply match themselves.  You can
  27 concatenate ordinary characters, so last matches the string 'last'.
  28
  29 The 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
  59 The special sequences consist of "\\" and a character from the list
  60 below.  If the ordinary character is not on the list, then the
  61 resulting 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
  77 This 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
  89 Some 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
 100 This module also defines an exception 'error'.
 101
 102 """
 103
 104 import sys
 105 import sre_compile
 106 import 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
 117 I = IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
 118 L = LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
 119 U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode locale
 120 M = MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
 121 S = DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
 122 X = VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
 123
 124 # sre extensions (experimental, don't rely on these)
 125 T = TEMPLATE = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
 126 DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation
 127
 128 # sre exception
 129 error = sre_compile.error
 130
 131 # --------------------------------------------------------------------
 132 # public interface
 133
 134 def 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
 139 def 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
 144 def 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 callable, it's passed the match object and must return
 149     a replacement string to be used."""
 150     return _compile(pattern, 0).sub(repl, string, count)
 151
 152 def subn(pattern, repl, string, count=0):
 153     """Return a 2-tuple containing (new_string, number).
 154     new_string is the string obtained by replacing the leftmost
 155     non-overlapping occurrences of the pattern in the source
 156     string by the replacement repl.  number is the number of
 157     substitutions that were made. repl can be either a string or a
 158     callable; if a callable, it's passed the match object and must
 159     return a replacement string to be used."""
 160     return _compile(pattern, 0).subn(repl, string, count)
 161
 162 def split(pattern, string, maxsplit=0):
 163     """Split the source string by the occurrences of the pattern,
 164     returning a list containing the resulting substrings."""
 165     return _compile(pattern, 0).split(string, maxsplit)
 166
 167 def findall(pattern, string, flags=0):
 168     """Return a list of all non-overlapping matches in the string.
 169
 170     If one or more groups are present in the pattern, return a
 171     list of groups; this will be a list of tuples if the pattern
 172     has more than one group.
 173
 174     Empty matches are included in the result."""
 175     return _compile(pattern, flags).findall(string)
 176
 177 if sys.hexversion >= 0x02020000:
 178     __all__.append("finditer")
 179     def finditer(pattern, string, flags=0):
 180         """Return an iterator over all non-overlapping matches in the
 181         string.  For each match, the iterator returns a match object.
 182
 183         Empty matches are included in the result."""
 184         return _compile(pattern, flags).finditer(string)
 185
 186 def compile(pattern, flags=0):
 187     "Compile a regular expression pattern, returning a pattern object."
 188     return _compile(pattern, flags)
 189
 190 def purge():
 191     "Clear the regular expression cache"
 192     _cache.clear()
 193     _cache_repl.clear()
 194
 195 def template(pattern, flags=0):
 196     "Compile a template pattern, returning a pattern object"
 197     return _compile(pattern, flags|T)
 198
 199 _alphanum = {}
 200 for c in 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890':
 201     _alphanum[c] = 1
 202 del c
 203
 204 def escape(pattern):
 205     "Escape all non-alphanumeric characters in pattern."
 206     s = list(pattern)
 207     alphanum = _alphanum
 208     for i in range(len(pattern)):
 209         c = pattern[i]
 210         if c not in alphanum:
 211             if c == "\000":
 212                 s[i] = "\\000"
 213             else:
 214                 s[i] = "\\" + c
 215     return pattern[:0].join(s)
 216
 217 # --------------------------------------------------------------------
 218 # internals
 219
 220 _cache = {}
 221 _cache_repl = {}
 222
 223 _pattern_type = type(sre_compile.compile("", 0))
 224
 225 _MAXCACHE = 100
 226
 227 def _compile(*key):
 228     # internal: compile pattern
 229     cachekey = (type(key[0]),) + key
 230     p = _cache.get(cachekey)
 231     if p is not None:
 232         return p
 233     pattern, flags = key
 234     if isinstance(pattern, _pattern_type):
 235         if flags:
 236             raise ValueError('Cannot process flags argument with a compiled pattern')
 237         return pattern
 238     if not sre_compile.isstring(pattern):
 239         raise TypeError, "first argument must be string or compiled pattern"
 240     try:
 241         p = sre_compile.compile(pattern, flags)
 242     except error, v:
 243         raise error, v # invalid expression
 244     if len(_cache) >= _MAXCACHE:
 245         _cache.clear()
 246     _cache[cachekey] = p
 247     return p
 248
 249 def _compile_repl(*key):
 250     # internal: compile replacement pattern
 251     p = _cache_repl.get(key)
 252     if p is not None:
 253         return p
 254     repl, pattern = key
 255     try:
 256         p = sre_parse.parse_template(repl, pattern)
 257     except error, v:
 258         raise error, v # invalid expression
 259     if len(_cache_repl) >= _MAXCACHE:
 260         _cache_repl.clear()
 261     _cache_repl[key] = p
 262     return p
 263
 264 def _expand(pattern, match, template):
 265     # internal: match.expand implementation hook
 266     template = sre_parse.parse_template(template, pattern)
 267     return sre_parse.expand_template(template, match)
 268
 269 def _subx(pattern, template):
 270     # internal: pattern.sub/subn implementation helper
 271     template = _compile_repl(template, pattern)
 272     if not template[0] and len(template[1]) == 1:
 273         # literal replacement
 274         return template[1][0]
 275     def filter(match, template=template):
 276         return sre_parse.expand_template(template, match)
 277     return filter
 278
 279 # register myself for pickling
 280
 281 import copy_reg
 282
 283 def _pickle(p):
 284     return _compile, (p.pattern, p.flags)
 285
 286 copy_reg.pickle(_pattern_type, _pickle, _compile)
 287
 288 # --------------------------------------------------------------------
 289 # experimental stuff (see python-dev discussions for details)
 290
 291 class Scanner:
 292     def __init__(self, lexicon, flags=0):
 293         from sre_constants import BRANCH, SUBPATTERN
 294         self.lexicon = lexicon
 295         # combine phrases into a compound pattern
 296         p = []
 297         s = sre_parse.Pattern()
 298         s.flags = flags
 299         for phrase, action in lexicon:
 300             p.append(sre_parse.SubPattern(s, [
 301                 (SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
 302                 ]))
 303         s.groups = len(p)+1
 304         p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
 305         self.scanner = sre_compile.compile(p)
 306     def scan(self, string):
 307         result = []
 308         append = result.append
 309         match = self.scanner.scanner(string).match
 310         i = 0
 311         while 1:
 312             m = match()
 313             if not m:
 314                 break
 315             j = m.end()
 316             if i == j:
 317                 break
 318             action = self.lexicon[m.lastindex-1][1]
 319             if hasattr(action, '__call__'):
 320                 self.match = m
 321                 action = action(self, m.group())
 322             if action is not None:
 323                 append(action)
 324             i = j
 325         return result, string[i:]