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gh-73267: Fix tm_yday in time.strptime() when a week rolls over a year #161828

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gh-73267: Fix tm_yday in time.strptime() when a week rolls over a year #161828

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5 changes: 5 additions & 0 deletions Lib/_strptime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -777,6 +777,11 @@ def parse_int(s):
year -= 1
yday = 366 if calendar.isleap(year) else 365
julian += yday
elif julian is not None:
yday = 366 if calendar.isleap(year) else 365
if julian > yday:
year += 1
julian -= yday

if julian is None:
# Cannot pre-calculate datetime_date() since can change in Julian
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13 changes: 13 additions & 0 deletions Lib/test/test_strptime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -873,6 +873,19 @@ def check(value, format, *expected):
check('2009 0 6', '%Y %W %w', 2009, 1, 3, 0, 0, 0, 5, 3)
check('2009 1 7', '%G %V %u', 2009, 1, 4, 0, 0, 0, 6, 4)

def test_last_week(self):
def check(value, format, *expected):
self.assertEqual(_strptime._strptime_time(value, format)[:-1], expected)
check('2018 53 1', '%Y %W %w', 2018, 12, 31, 0, 0, 0, 0, 365)
check('2018 53 2', '%Y %W %w', 2019, 1, 1, 0, 0, 0, 1, 1)
check('2015 52 4', '%Y %U %w', 2015, 12, 31, 0, 0, 0, 3, 365)
check('2015 52 5', '%Y %U %w', 2016, 1, 1, 0, 0, 0, 4, 1)

check('2012 53 1', '%Y %U %w', 2012, 12, 31, 0, 0, 0, 0, 366)
check('2012 53 2', '%Y %U %w', 2013, 1, 1, 0, 0, 0, 1, 1)
check('2016 52 6', '%Y %W %w', 2016, 12, 31, 0, 0, 0, 5, 366)
check('2016 52 0', '%Y %W %w', 2017, 1, 1, 0, 0, 0, 6, 1)


class CacheTests(unittest.TestCase):
"""Test that caching works properly."""
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-11-11-16-09-46.gh-issue-73267.64jTqg.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :func:`time.strptime` returning a ``tm_yday`` that did not match the
date when a week number (``%U`` or ``%W``) and a weekday resolved to a date
in the next year.