Python----re.py

Posted 2020-06-24

  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 ([email protected]).
 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 try:
108     import _locale
109 except ImportError:
110     _locale = None
111 
112 # public symbols
113 __all__ = [ "match", "search", "sub", "subn", "split", "findall",
114     "compile", "purge", "template", "escape", "I", "L", "M", "S", "X",
115     "U", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
116     "UNICODE", "error" ]
117 
118 __version__ = "2.2.1"
119 
120 # flags
121 I = IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
122 L = LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
123 U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode locale
124 M = MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
125 S = DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
126 X = VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
127 
128 # sre extensions (experimental, don‘t rely on these)
129 T = TEMPLATE = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
130 DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation
131 
132 # sre exception
133 error = sre_compile.error
134 
135 # --------------------------------------------------------------------
136 # public interface
137 
138 def match(pattern, string, flags=0):
139     """Try to apply the pattern at the start of the string, returning
140     a match object, or None if no match was found."""
141     return _compile(pattern, flags).match(string)
142 
143 def search(pattern, string, flags=0):
144     """Scan through string looking for a match to the pattern, returning
145     a match object, or None if no match was found."""
146     return _compile(pattern, flags).search(string)
147 
148 def sub(pattern, repl, string, count=0, flags=0):
149     """Return the string obtained by replacing the leftmost
150     non-overlapping occurrences of the pattern in string by the
151     replacement repl.  repl can be either a string or a callable;
152     if a string, backslash escapes in it are processed.  If it is
153     a callable, it‘s passed the match object and must return
154     a replacement string to be used."""
155     return _compile(pattern, flags).sub(repl, string, count)
156 
157 def subn(pattern, repl, string, count=0, flags=0):
158     """Return a 2-tuple containing (new_string, number).
159     new_string is the string obtained by replacing the leftmost
160     non-overlapping occurrences of the pattern in the source
161     string by the replacement repl.  number is the number of
162     substitutions that were made. repl can be either a string or a
163     callable; if a string, backslash escapes in it are processed.
164     If it is a callable, it‘s passed the match object and must
165     return a replacement string to be used."""
166     return _compile(pattern, flags).subn(repl, string, count)
167 
168 def split(pattern, string, maxsplit=0, flags=0):
169     """Split the source string by the occurrences of the pattern,
170     returning a list containing the resulting substrings."""
171     return _compile(pattern, flags).split(string, maxsplit)
172 
173 def findall(pattern, string, flags=0):
174     """Return a list of all non-overlapping matches in the string.
175 
176     If one or more groups are present in the pattern, return a
177     list of groups; this will be a list of tuples if the pattern
178     has more than one group.
179 
180     Empty matches are included in the result."""
181     return _compile(pattern, flags).findall(string)
182 
183 if sys.hexversion >= 0x02020000:
184     __all__.append("finditer")
185     def finditer(pattern, string, flags=0):
186         """Return an iterator over all non-overlapping matches in the
187         string.  For each match, the iterator returns a match object.
188 
189         Empty matches are included in the result."""
190         return _compile(pattern, flags).finditer(string)
191 
192 def compile(pattern, flags=0):
193     "Compile a regular expression pattern, returning a pattern object."
194     return _compile(pattern, flags)
195 
196 def purge():
197     "Clear the regular expression cache"
198     _cache.clear()
199     _cache_repl.clear()
200 
201 def template(pattern, flags=0):
202     "Compile a template pattern, returning a pattern object"
203     return _compile(pattern, flags|T)
204 
205 _alphanum = frozenset(
206     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
207 
208 def escape(pattern):
209     "Escape all non-alphanumeric characters in pattern."
210     s = list(pattern)
211     alphanum = _alphanum
212     for i, c in enumerate(pattern):
213         if c not in alphanum:
214             if c == "\000":
215                 s[i] = "\\000"
216             else:
217                 s[i] = "\\" + c
218     return pattern[:0].join(s)
219 
220 # --------------------------------------------------------------------
221 # internals
222 
223 _cache = {}
224 _cache_repl = {}
225 
226 _pattern_type = type(sre_compile.compile("", 0))
227 
228 _MAXCACHE = 100
229 
230 def _compile(*key):
231     # internal: compile pattern
232     pattern, flags = key
233     bypass_cache = flags & DEBUG
234     if not bypass_cache:
235         cachekey = (type(key[0]),) + key
236         try:
237             p, loc = _cache[cachekey]
238             if loc is None or loc == _locale.setlocale(_locale.LC_CTYPE):
239                 return p
240         except KeyError:
241             pass
242     if isinstance(pattern, _pattern_type):
243         if flags:
244             raise ValueError(‘Cannot process flags argument with a compiled pattern‘)
245         return pattern
246     if not sre_compile.isstring(pattern):
247         raise TypeError, "first argument must be string or compiled pattern"
248     try:
249         p = sre_compile.compile(pattern, flags)
250     except error, v:
251         raise error, v # invalid expression
252     if not bypass_cache:
253         if len(_cache) >= _MAXCACHE:
254             _cache.clear()
255         if p.flags & LOCALE:
256             if not _locale:
257                 return p
258             loc = _locale.setlocale(_locale.LC_CTYPE)
259         else:
260             loc = None
261         _cache[cachekey] = p, loc
262     return p
263 
264 def _compile_repl(*key):
265     # internal: compile replacement pattern
266     p = _cache_repl.get(key)
267     if p is not None:
268         return p
269     repl, pattern = key
270     try:
271         p = sre_parse.parse_template(repl, pattern)
272     except error, v:
273         raise error, v # invalid expression
274     if len(_cache_repl) >= _MAXCACHE:
275         _cache_repl.clear()
276     _cache_repl[key] = p
277     return p
278 
279 def _expand(pattern, match, template):
280     # internal: match.expand implementation hook
281     template = sre_parse.parse_template(template, pattern)
282     return sre_parse.expand_template(template, match)
283 
284 def _subx(pattern, template):
285     # internal: pattern.sub/subn implementation helper
286     template = _compile_repl(template, pattern)
287     if not template[0] and len(template[1]) == 1:
288         # literal replacement
289         return template[1][0]
290     def filter(match, template=template):
291         return sre_parse.expand_template(template, match)
292     return filter
293 
294 # register myself for pickling
295 
296 import copy_reg
297 
298 def _pickle(p):
299     return _compile, (p.pattern, p.flags)
300 
301 copy_reg.pickle(_pattern_type, _pickle, _compile)
302 
303 # --------------------------------------------------------------------
304 # experimental stuff (see python-dev discussions for details)
305 
306 class Scanner:
307     def __init__(self, lexicon, flags=0):
308         from sre_constants import BRANCH, SUBPATTERN
309         self.lexicon = lexicon
310         # combine phrases into a compound pattern
311         p = []
312         s = sre_parse.Pattern()
313         s.flags = flags
314         for phrase, action in lexicon:
315             p.append(sre_parse.SubPattern(s, [
316                 (SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
317                 ]))
318         s.groups = len(p)+1
319         p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
320         self.scanner = sre_compile.compile(p)
321     def scan(self, string):
322         result = []
323         append = result.append
324         match = self.scanner.scanner(string).match
325         i = 0
326         while 1:
327             m = match()
328             if not m:
329                 break
330             j = m.end()
331             if i == j:
332                 break
333             action = self.lexicon[m.lastindex-1][1]
334             if hasattr(action, ‘__call__‘):
335                 self.match = m
336                 action = action(self, m.group())
337             if action is not None:
338                 append(action)
339             i = j
340         return result, string[i:]

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