re

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# Source Code for Module re

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