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
17r"""Support for regular expressions (RE).
18
19This module provides regular expression matching operations similar to
20those found in Perl.  It supports both 8-bit and Unicode strings; both
21the pattern and the strings being processed can contain null bytes and
22characters outside the US ASCII range.
23
24Regular expressions can contain both special and ordinary characters.
25Most ordinary characters, like "A", "a", or "0", are the simplest
26regular expressions; they simply match themselves.  You can
27concatenate ordinary characters, so last matches the string 'last'.
28
29The 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
59The special sequences consist of "\\" and a character from the list
60below.  If the ordinary character is not on the list, then the
61resulting 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
77This 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
89Some 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
100This module also defines an exception 'error'.
101
102"""
103
104import sys
105import sre_compile
106import 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
117I = IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
118L = LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
119U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode locale
120M = MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
121S = DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
122X = VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
123
124# sre extensions (experimental, don't rely on these)
125T = TEMPLATE = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
126DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation
127
128# sre exception
129error = sre_compile.error
130
131# --------------------------------------------------------------------
132# public interface
133
134def 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
139def 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
144def 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
153def 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
164def 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
169def 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
179if 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
188def compile(pattern, flags=0):
189    "Compile a regular expression pattern, returning a pattern object."
190    return _compile(pattern, flags)
191
192def purge():
193    "Clear the regular expression cache"
194    _cache.clear()
195    _cache_repl.clear()
196
197def template(pattern, flags=0):
198    "Compile a template pattern, returning a pattern object"
199    return _compile(pattern, flags|T)
200
201_alphanum = frozenset(
202    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
203
204def escape(pattern):
205    "Escape all non-alphanumeric characters in pattern."
206    s = list(pattern)
207    alphanum = _alphanum
208    for i, c in enumerate(pattern):
209        if c not in alphanum:
210            if c == "\000":
211                s[i] = "\\000"
212            else:
213                s[i] = "\\" + c
214    return pattern[:0].join(s)
215
216# --------------------------------------------------------------------
217# internals
218
219_cache = {}
220_cache_repl = {}
221
222_pattern_type = type(sre_compile.compile("", 0))
223
224_MAXCACHE = 100
225
226def _compile(*key):
227    # internal: compile pattern
228    cachekey = (type(key[0]),) + key
229    p = _cache.get(cachekey)
230    if p is not None:
231        return p
232    pattern, flags = key
233    if isinstance(pattern, _pattern_type):
234        if flags:
235            raise ValueError('Cannot process flags argument with a compiled pattern')
236        return pattern
237    if not sre_compile.isstring(pattern):
238        raise TypeError, "first argument must be string or compiled pattern"
239    try:
240        p = sre_compile.compile(pattern, flags)
241    except error, v:
242        raise error, v # invalid expression
243    if len(_cache) >= _MAXCACHE:
244        _cache.clear()
245    _cache[cachekey] = p
246    return p
247
248def _compile_repl(*key):
249    # internal: compile replacement pattern
250    p = _cache_repl.get(key)
251    if p is not None:
252        return p
253    repl, pattern = key
254    try:
255        p = sre_parse.parse_template(repl, pattern)
256    except error, v:
257        raise error, v # invalid expression
258    if len(_cache_repl) >= _MAXCACHE:
259        _cache_repl.clear()
260    _cache_repl[key] = p
261    return p
262
263def _expand(pattern, match, template):
264    # internal: match.expand implementation hook
265    template = sre_parse.parse_template(template, pattern)
266    return sre_parse.expand_template(template, match)
267
268def _subx(pattern, template):
269    # internal: pattern.sub/subn implementation helper
270    template = _compile_repl(template, pattern)
271    if not template[0] and len(template[1]) == 1:
272        # literal replacement
273        return template[1][0]
274    def filter(match, template=template):
275        return sre_parse.expand_template(template, match)
276    return filter
277
278# register myself for pickling
279
280import copy_reg
281
282def _pickle(p):
283    return _compile, (p.pattern, p.flags)
284
285copy_reg.pickle(_pattern_type, _pickle, _compile)
286
287# --------------------------------------------------------------------
288# experimental stuff (see python-dev discussions for details)
289
290class Scanner:
291    def __init__(self, lexicon, flags=0):
292        from sre_constants import BRANCH, SUBPATTERN
293        self.lexicon = lexicon
294        # combine phrases into a compound pattern
295        p = []
296        s = sre_parse.Pattern()
297        s.flags = flags
298        for phrase, action in lexicon:
299            p.append(sre_parse.SubPattern(s, [
300                (SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
301                ]))
302        s.groups = len(p)+1
303        p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
304        self.scanner = sre_compile.compile(p)
305    def scan(self, string):
306        result = []
307        append = result.append
308        match = self.scanner.scanner(string).match
309        i = 0
310        while 1:
311            m = match()
312            if not m:
313                break
314            j = m.end()
315            if i == j:
316                break
317            action = self.lexicon[m.lastindex-1][1]
318            if hasattr(action, '__call__'):
319                self.match = m
320                action = action(self, m.group())
321            if action is not None:
322                append(action)
323            i = j
324        return result, string[i:]
325