gh-93671: Avoid exponential backtracking in deeply nested sequence patterns in match statements by pablogsal · Pull Request #93680 · python/cpython · GitHub
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gh-93671: Avoid exponential backtracking in deeply nested sequence patterns in match statements #93680

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Merged
ambv merged 2 commits into from
Jun 10, 2022
Merged

gh-93671: Avoid exponential backtracking in deeply nested sequence patterns in match statements #93680

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gh-93671: Avoid exponential backtracking in deeply nested sequence pa…
pablogsal Jun 10, 2022
9907737
s/patters/patterns/
ambv Jun 10, 2022
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6 changes: 3 additions & 3 deletions Grammar/python.gram
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21 changes: 21 additions & 0 deletions Lib/test/test_patma.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3151,6 +3151,27 @@ def f(command): # 0
self.assertListEqual(self._trace(f, "go x"), [1, 2, 3])
self.assertListEqual(self._trace(f, "spam"), [1, 2, 3])

def test_parser_deeply_nested_patterns(self):
# Deeply nested patterns can cause exponential backtracking when parsing.
# See gh-93671 for more information.

levels = 100

patterns = [
"A" + "(" * levels + ")" * levels,
"{1:" * levels + "1" + "}" * levels,
"[" * levels + "1" + "]" * levels,
]

for pattern in patterns:
with self.subTest(pattern):
code = inspect.cleandoc("""
match None:
case {}:
pass
""".format(pattern))
compile(code, "<string>", "exec")


if __name__ == "__main__":
"""
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-06-10-12-03-17.gh-issue-93671.idkQqG.rst
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10 changes: 10 additions & 0 deletions Parser/parser.c
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