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gh-136065: Fix quadratic complexity in os.path.expandvars() (GH-134952)

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Co-authored-by: Łukasz Langa <lukasz@langa.pl>
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Serhiy Storchaka 2025-10-31 15:49:51 +02:00 • committed by GitHub
parent 81cec22a9b
commit f029e8db62
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5 changed files with 96 additions and 116 deletions
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21
Lib/test/test_ntpath.py
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@ -9,7 +9,7 @@
import warnings
from ntpath import ALL_BUT_LAST, ALLOW_MISSING
from test import support
from test.support import TestFailed, cpython_only, os_helper
from test.support import os_helper
from test.support.os_helper import FakePath
from test import test_genericpath
from tempfile import TemporaryFile
@ -59,7 +59,7 @@ def tester(fn, wantResult):
fn = fn.replace("\\", "\\\\")
gotResult = eval(fn)
if wantResult != gotResult and _norm(wantResult) != _norm(gotResult):
raise TestFailed("%s should return: %s but returned: %s" \
raise support.TestFailed("%s should return: %s but returned: %s" \
%(str(fn), str(wantResult), str(gotResult)))
# then with bytes
@ -75,7 +75,7 @@ def tester(fn, wantResult):
warnings.simplefilter("ignore", DeprecationWarning)
gotResult = eval(fn)
if _norm(wantResult) != _norm(gotResult):
raise TestFailed("%s should return: %s but returned: %s" \
raise support.TestFailed("%s should return: %s but returned: %s" \
%(str(fn), str(wantResult), repr(gotResult)))
@ -1133,6 +1133,19 @@ def check(value, expected):
check('%spam%bar', '%sbar' % nonascii)
check('%{}%bar'.format(nonascii), 'ham%sbar' % nonascii)
@support.requires_resource('cpu')
def test_expandvars_large(self):
expandvars = ntpath.expandvars
with os_helper.EnvironmentVarGuard() as env:
env.clear()
env["A"] = "B"
n = 100_000
self.assertEqual(expandvars('%A%'*n), 'B'*n)
self.assertEqual(expandvars('%A%A'*n), 'BA'*n)
self.assertEqual(expandvars("''"*n + '%%'), "''"*n + '%')
self.assertEqual(expandvars("%%"*n), "%"*n)
self.assertEqual(expandvars("$$"*n), "$"*n)
def test_expanduser(self):
tester('ntpath.expanduser("test")', 'test')
@ -1550,7 +1563,7 @@ def test_con_device(self):
self.assertTrue(os.path.exists(r"\\.\CON"))
@unittest.skipIf(sys.platform != 'win32', "Fast paths are only for win32")
@cpython_only
@support.cpython_only
def test_fast_paths_in_use(self):
# There are fast paths of these functions implemented in posixmodule.c.
# Confirm that they are being used, and not the Python fallbacks in