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bpo-40480: restore ability to join fnmatch.translate() results #20049

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Merged
merged 3 commits into from
May 12, 2020
Merged

bpo-40480: restore ability to join fnmatch.translate() results #20049

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42b0cdd
In translate(), generate unique group names across calls.
tim-one May 12, 2020
002baa6
Not sure why I have to do this again :-(
tim-one May 12, 2020
770ec51
Repair comment.
tim-one May 12, 2020
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17 changes: 13 additions & 4 deletions Lib/fnmatch.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,12 @@

__all__ = ["filter", "fnmatch", "fnmatchcase", "translate"]

# Build a thread-safe incrementing counter to help create unique regexp group
# names across calls.
from itertools import count
_nextgroupnum = count().__next__
del count

def fnmatch(name, pat):
"""Test whether FILENAME matches PATTERN.

Expand Down Expand Up @@ -148,9 +154,12 @@ def translate(pat):
# in a lookahead assertion, save the matched part in a group, then
# consume that group via a backreference. If the overall match fails,
# the lookahead assertion won't try alternatives. So the translation is:
# (?=(P<name>.*?fixed))(?P=name)
# Group names are created as needed: g1, g2, g3, ...
groupnum = 0
# (?=(?P<name>.*?fixed))(?P=name)
# Group names are created as needed: g0, g1, g2, ...
# The numbers are obtained from _nextgroupnum() to ensure they're unique
# across calls and across threads. This is because people rely on the
# undocumented ability to join multiple translate() results together via
# "|" to build large regexps matching "one of many" shell patterns.
while i < n:
assert inp[i] is STAR
i += 1
Expand All @@ -167,7 +176,7 @@ def translate(pat):
add(".*")
add(fixed)
else:
groupnum += 1
groupnum = _nextgroupnum()
add(f"(?=(?P<g{groupnum}>.*?{fixed}))(?P=g{groupnum})")
assert i == n
res = "".join(res)
Expand Down
24 changes: 21 additions & 3 deletions Lib/test/test_fnmatch.py
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Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,7 @@ def test_warnings(self):
class TranslateTestCase(unittest.TestCase):

def test_translate(self):
import re
self.assertEqual(translate('*'), r'(?s:.*)\Z')
self.assertEqual(translate('?'), r'(?s:.)\Z')
self.assertEqual(translate('a?b*'), r'(?s:a.b.*)\Z')
Expand All @@ -122,9 +123,26 @@ def test_translate(self):
self.assertEqual(translate('*********A'), r'(?s:.*A)\Z')
self.assertEqual(translate('A*********?[?]?'), r'(?s:A.*.[?].)\Z')
# fancy translation to prevent exponential-time match failure
self.assertEqual(translate('**a*a****a'),
r'(?s:(?=(?P<g1>.*?a))(?P=g1)(?=(?P<g2>.*?a))(?P=g2).*a)\Z')

t = translate('**a*a****a')
digits = re.findall(r'\d+', t)
self.assertEqual(len(digits), 4)
self.assertEqual(digits[0], digits[1])
self.assertEqual(digits[2], digits[3])
g1 = f"g{digits[0]}" # e.g., group name "g4"
g2 = f"g{digits[2]}" # e.g., group name "g5"
self.assertEqual(t,
fr'(?s:(?=(?P<{g1}>.*?a))(?P={g1})(?=(?P<{g2}>.*?a))(?P={g2}).*a)\Z')
# and try pasting multiple translate results - it's an undocumented
# feature that this works; all the pain of generating unique group
# names across calls exists to support this
r1 = translate('**a**a**a*')
r2 = translate('**b**b**b*')
r3 = translate('*c*c*c*')
fatre = "|".join([r1, r2, r3])
self.assertTrue(re.match(fatre, 'abaccad'))
self.assertTrue(re.match(fatre, 'abxbcab'))
self.assertTrue(re.match(fatre, 'cbabcaxc'))
self.assertFalse(re.match(fatre, 'dabccbad'))

class FilterTestCase(unittest.TestCase):

Expand Down