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Test failure in test_find_periodic_pattern in string_tests.py #105639
Description
A recent test failure:
FAIL: test_find_periodic_pattern (test.test_bytes.ByteArrayAsStringTest.test_find_periodic_pattern) (p='', text='')
Cover the special path for periodic patterns.
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Traceback (most recent call last):
File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/string_tests.py", line 335, in test_find_periodic_pattern
self.checkequal(reference_find(p, text),
File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/string_tests.py", line 60, in checkequal
self.assertEqual(
AssertionError: -1 != 0
The issue is reference_find:
def reference_find(p, s):
for i in range(len(s)):
if s.startswith(p, i):
return i
return -1
When s == p == '', we get for i in range(0), and then -1 is returned instead of the actual result which should be 0.
Activity
terryjreedy commentedon Jun 11, 2023
My immediate question was "What could have happened that this should suddenly fail?" The answer is "Nothing!" For each CI run, reference_find is called 1000 times with random input. There is obviously a non-zero probabilty of generating this corner case for which the test as a whole is wrong. Hence we get an occasional bogus failure. Some possible fixes:
if not p or not text: continueaftertextis generated, or perhapsif not p: continueafterpis generated.The test was added in #86138, with PR by Dennis Sweeny and Tim Peters.
hugovk commentedon Mar 7, 2025
Thanks for the report, however it's been subsequently resolved by PR #110170 and issue #110160.