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 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          return pattern
    236      if not sre_compile.isstring(pattern):
    237          raise TypeError, "first argument must be string or compiled pattern"
    238      try:
    239          p = sre_compile.compile(pattern, flags)
    240      except error, v:
    241          raise error, v # invalid expression
    242      if len(_cache) >= _MAXCACHE:
    243          _cache.clear()
    244      _cache[cachekey] = p
    245      return p
    246
    247 -def _compile_repl(*key):
    248      # internal: compile replacement pattern
    249      p = _cache_repl.get(key)
    250      if p is not None:
    251          return p
    252      repl, pattern = key
    253      try:
    254          p = sre_parse.parse_template(repl, pattern)
    255      except error, v:
    256          raise error, v # invalid expression
    257      if len(_cache_repl) >= _MAXCACHE:
    258          _cache_repl.clear()
    259      _cache_repl[key] = p
    260      return p
    261
    262 -def _expand(pattern, match, template):
    263      # internal: match.expand implementation hook
    264      template = sre_parse.parse_template(template, pattern)
    265      return sre_parse.expand_template(template, match)
    266
    267 -def _subx(pattern, template):
    268      # internal: pattern.sub/subn implementation helper
    269      template = _compile_repl(template, pattern)
    270      if not template[0] and len(template[1]) == 1:
    271          # literal replacement
    272          return template[1][0]
    273      def filter(match, template=template):
    274          return sre_parse.expand_template(template, match)
    275      return filter
    276
    277  # register myself for pickling
    278
    279  import copy_reg
    280
    281 -def _pickle(p):
    282      return _compile, (p.pattern, p.flags)
    283
    284  copy_reg.pickle(_pattern_type, _pickle, _compile)
    285
    286  # --------------------------------------------------------------------
    287  # experimental stuff (see python-dev discussions for details)
    288
    289 -class Scanner:
    290 -    def __init__(self, lexicon, flags=0):
    291          from sre_constants import BRANCH, SUBPATTERN
    292          self.lexicon = lexicon
    293          # combine phrases into a compound pattern
    294          p = []
    295          s = sre_parse.Pattern()
    296          s.flags = flags
    297          for phrase, action in lexicon:
    298              p.append(sre_parse.SubPattern(s, [
    299                  (SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
    300                  ]))
    301          s.groups = len(p)+1
    302          p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
    303          self.scanner = sre_compile.compile(p)
    304 -    def scan(self, string):
    305          result = []
    306          append = result.append
    307          match = self.scanner.scanner(string).match
    308          i = 0
    309          while 1:
    310              m = match()
    311              if not m:
    312                  break
    313              j = m.end()
    314              if i == j:
    315                  break
    316              action = self.lexicon[m.lastindex-1][1]
    317              if callable(action):
    318                  self.match = m
    319                  action = action(self, m.group())
    320              if action is not None:
    321                  append(action)
    322              i = j
    323          return result, string[i:]
    324