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, flags=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, flags).sub(repl, string, count)
 152
 153 def subn(pattern, repl, string, count=0, flags=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, flags).subn(repl, string, count)
 163
 164 def split(pattern, string, maxsplit=0, flags=0):
 165     """Split the source string by the occurrences of the pattern,
 166     returning a list containing the resulting substrings."""
 167     return _compile(pattern, flags).split(string, maxsplit)
 168
 169 def 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
 179 if 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
 188 def compile(pattern, flags=0):
 189     "Compile a regular expression pattern, returning a pattern object."
 190     return _compile(pattern, flags)
 191
 192 def purge():
 193     "Clear the regular expression cache"
 194     _cache.clear()
 195     _cache_repl.clear()
 196
 197 def template(pattern, flags=0):
 198     "Compile a template pattern, returning a pattern object"
 199     return _compile(pattern, flags|T)
 200
 201 _alphanum = {}
 202 for c in 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890':
 203     _alphanum[c] = 1
 204 del c
 205
 206 def 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
 229 def _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
 251 def _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
 266 def _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
 271 def _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
 283 import copy_reg
 284
 285 def _pickle(p):
 286     return _compile, (p.pattern, p.flags)
 287
 288 copy_reg.pickle(_pattern_type, _pickle, _compile)
 289
 290 # --------------------------------------------------------------------
 291 # experimental stuff (see python-dev discussions for details)
 292
 293 class 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:]