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 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
    153 -def 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
    164 -def 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
    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:]
    328