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Issues #814253, #9179: Group references and conditional group references now 

work in lookbehind assertions in regular expressions.
This commit is contained in:
Serhiy Storchaka 2015-02-21 10:07:35 +02:00
parent df80706f14
commit 4eea62fd2e
5 changed files with 92 additions and 12 deletions
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3
Doc/library/re.rst
View File

@ -297,6 +297,9 @@ The special characters are:
>>> m.group(0)
'egg'
.. versionchanged: 3.5
Added support for group references of fixed length.
``(?<!...)``
Matches if the current position in the string is not preceded by a match for
``...``. This is called a :dfn:`negative lookbehind assertion`. Similar to

5
Lib/re.py
View File

@ -351,10 +351,11 @@ class Scanner:
s = sre_parse.Pattern()
s.flags = flags
for phrase, action in lexicon:
gid = s.opengroup()
p.append(sre_parse.SubPattern(s, [
(SUBPATTERN, (len(p)+1, sre_parse.parse(phrase, flags))),
(SUBPATTERN, (gid, sre_parse.parse(phrase, flags))),
]))
s.groups = len(p)+1
s.closegroup(gid, p[-1])
p = sre_parse.SubPattern(s, [(BRANCH, (None, p))])
self.scanner = sre_compile.compile(p)
def scan(self, string):

51
Lib/sre_parse.py
View File

@ -68,12 +68,15 @@ class Pattern:
# master pattern object. keeps track of global attributes
def __init__(self):
self.flags = 0
self.open = []
self.groups = 1
self.groupdict = {}
self.subpatterns = [None] # group 0
self.lookbehindgroups = None
@property
def groups(self):
return len(self.subpatterns)
def opengroup(self, name=None):
gid = self.groups
self.groups = gid + 1
self.subpatterns.append(None)
if self.groups > MAXGROUPS:
raise error("groups number is too large")
if name is not None:
@ -82,12 +85,19 @@ class Pattern:
raise error("redefinition of group name %r as group %d; "
"was group %d" % (name, gid, ogid))
self.groupdict[name] = gid
self.open.append(gid)
return gid
def closegroup(self, gid):
self.open.remove(gid)
def closegroup(self, gid, p):
self.subpatterns[gid] = p
def checkgroup(self, gid):
return gid < self.groups and gid not in self.open
return gid < self.groups and self.subpatterns[gid] is not None
def checklookbehindgroup(self, gid, source):
if self.lookbehindgroups is not None:
if not self.checkgroup(gid):
raise source.error('cannot refer to an open group')
if gid >= self.lookbehindgroups:
raise source.error('cannot refer to group defined in the same '
'lookbehind subpattern')
class SubPattern:
# a subpattern, in intermediate form
@ -183,7 +193,21 @@ class SubPattern:
elif op in _UNITCODES:
lo = lo + 1
hi = hi + 1
elif op == SUCCESS:
elif op is GROUPREF:
i, j = self.pattern.subpatterns[av].getwidth()
lo = lo + i
hi = hi + j
elif op is GROUPREF_EXISTS:
i, j = av[1].getwidth()
if av[2] is not None:
l, h = av[2].getwidth()
i = min(i, l)
j = max(j, h)
else:
i = 0
lo = lo + i
hi = hi + j
elif op is SUCCESS:
break
self.width = min(lo, MAXREPEAT - 1), min(hi, MAXREPEAT)
return self.width
@ -379,6 +403,7 @@ def _escape(source, escape, state):
if not state.checkgroup(group):
raise source.error("cannot refer to open group",
len(escape))
state.checklookbehindgroup(group, source)
return GROUPREF, group
raise ValueError
if len(escape) == 2:
@ -641,6 +666,7 @@ def _parse(source, state):
if gid is None:
msg = "unknown group name: {0!r}".format(name)
raise source.error(msg, len(name) + 1)
state.checklookbehindgroup(gid, source)
subpatternappend((GROUPREF, gid))
continue
else:
@ -668,7 +694,13 @@ def _parse(source, state):
if char is None or char not in "=!":
raise source.error("syntax error")
dir = -1 # lookbehind
lookbehindgroups = state.lookbehindgroups
if lookbehindgroups is None:
state.lookbehindgroups = state.groups
p = _parse_sub(source, state)
if dir < 0:
if lookbehindgroups is None:
state.lookbehindgroups = None
if not sourcematch(")"):
raise source.error("unbalanced parenthesis")
if char == "=":
@ -701,6 +733,7 @@ def _parse(source, state):
if condgroup >= MAXGROUPS:
raise source.error("the group number is too large",
len(condname) + 1)
state.checklookbehindgroup(condgroup, source)
elif char in FLAGS:
# flags
state.flags |= FLAGS[char]
@ -726,7 +759,7 @@ def _parse(source, state):
if not sourcematch(")"):
raise source.error("unbalanced parenthesis")
if group is not None:
state.closegroup(group)
state.closegroup(group, p)
subpatternappend((SUBPATTERN, (group, p)))
else:
while True:

42
Lib/test/test_re.py
View File

@ -604,7 +604,7 @@ class ReTests(unittest.TestCase):
self.assertEqual(re.match("a.*b", "a\n\nb", re.DOTALL).group(0),
"a\n\nb")
def test_non_consuming(self):
def test_lookahead(self):
self.assertEqual(re.match("(a(?=\s[^a]))", "a b").group(1), "a")
self.assertEqual(re.match("(a(?=\s[^a]*))", "a b").group(1), "a")
self.assertEqual(re.match("(a(?=\s[abc]))", "a b").group(1), "a")
@ -618,6 +618,46 @@ class ReTests(unittest.TestCase):
self.assertEqual(re.match(r"(a)(?!\s\1)", "a b").group(1), "a")
self.assertEqual(re.match(r"(a)(?!\s(abc|a))", "a b").group(1), "a")
# Group reference.
self.assertTrue(re.match(r'(a)b(?=\1)a', 'aba'))
self.assertIsNone(re.match(r'(a)b(?=\1)c', 'abac'))
# Conditional group reference.
self.assertTrue(re.match(r'(?:(a)|(x))b(?=(?(2)x|c))c', 'abc'))
self.assertIsNone(re.match(r'(?:(a)|(x))b(?=(?(2)c|x))c', 'abc'))
self.assertTrue(re.match(r'(?:(a)|(x))b(?=(?(2)x|c))c', 'abc'))
self.assertIsNone(re.match(r'(?:(a)|(x))b(?=(?(1)b|x))c', 'abc'))
self.assertTrue(re.match(r'(?:(a)|(x))b(?=(?(1)c|x))c', 'abc'))
# Group used before defined.
self.assertTrue(re.match(r'(a)b(?=(?(2)x|c))(c)', 'abc'))
self.assertIsNone(re.match(r'(a)b(?=(?(2)b|x))(c)', 'abc'))
self.assertTrue(re.match(r'(a)b(?=(?(1)c|x))(c)', 'abc'))
def test_lookbehind(self):
self.assertTrue(re.match(r'ab(?<=b)c', 'abc'))
self.assertIsNone(re.match(r'ab(?<=c)c', 'abc'))
self.assertIsNone(re.match(r'ab(?<!b)c', 'abc'))
self.assertTrue(re.match(r'ab(?<!c)c', 'abc'))
# Group reference.
self.assertTrue(re.match(r'(a)a(?<=\1)c', 'aac'))
self.assertIsNone(re.match(r'(a)b(?<=\1)a', 'abaa'))
self.assertIsNone(re.match(r'(a)a(?<!\1)c', 'aac'))
self.assertTrue(re.match(r'(a)b(?<!\1)a', 'abaa'))
# Conditional group reference.
self.assertIsNone(re.match(r'(?:(a)|(x))b(?<=(?(2)x|c))c', 'abc'))
self.assertIsNone(re.match(r'(?:(a)|(x))b(?<=(?(2)b|x))c', 'abc'))
self.assertTrue(re.match(r'(?:(a)|(x))b(?<=(?(2)x|b))c', 'abc'))
self.assertIsNone(re.match(r'(?:(a)|(x))b(?<=(?(1)c|x))c', 'abc'))
self.assertTrue(re.match(r'(?:(a)|(x))b(?<=(?(1)b|x))c', 'abc'))
# Group used before defined.
self.assertRaises(re.error, re.compile, r'(a)b(?<=(?(2)b|x))(c)')
self.assertIsNone(re.match(r'(a)b(?<=(?(1)c|x))(c)', 'abc'))
self.assertTrue(re.match(r'(a)b(?<=(?(1)b|x))(c)', 'abc'))
# Group defined in the same lookbehind pattern
self.assertRaises(re.error, re.compile, r'(a)b(?<=(.)\2)(c)')
self.assertRaises(re.error, re.compile, r'(a)b(?<=(?P<a>.)(?P=a))(c)')
self.assertRaises(re.error, re.compile, r'(a)b(?<=(a)(?(2)b|x))(c)')
self.assertRaises(re.error, re.compile, r'(a)b(?<=(.)(?<=\2))(c)')
def test_ignore_case(self):
self.assertEqual(re.match("abc", "ABC", re.I).group(0), "ABC")
self.assertEqual(re.match(b"abc", b"ABC", re.I).group(0), b"ABC")

3
Misc/NEWS
View File

@ -13,6 +13,9 @@ Core and Builtins
Library
-------
- Issues #814253, #9179: Group references and conditional group references now
work in lookbehind assertions in regular expressions.
- Issue #23215: Multibyte codecs with custom error handlers that ignores errors
consumed too much memory and raised SystemError or MemoryError.
Original patch by Aleksi Torhamo.