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gh-159714: Fix ZoneInfo Julian day 59 in leap years #159721

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Merged
StanFromIreland merged 1 commit into from
Oct 21, 2026
Merged

gh-159714: Fix ZoneInfo Julian day 59 in leap years #159721

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27 changes: 27 additions & 0 deletions Lib/test/test_zoneinfo/test_zoneinfo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1492,6 +1492,33 @@ def _add():
(datetime(2020, 12, 31, 23, 59, 59, 999999), AAA, NORMAL),
)

@call
def _add():
# Julian days 58, 59 and 60 always mean February 27, February 28
# and March 1, including in leap years.
AAA = ZoneOffset("AAA", ZERO)
BBB = ZoneOffset("BBB", ONE_H, ONE_H)

for start, end, start_date, end_date in (
(58, 59, (2, 27), (2, 28)),
(59, 60, (2, 28), (3, 1)),
):
tzstr = f"AAA0BBB,J{start}/12,J{end}/12"
cases[tzstr] = []
for year in (2019, 2020, 2000, 2100):
start_dt = datetime(year, *start_date, 12)
end_dt = datetime(year, *end_date, 12)
cases[tzstr].extend((
(start_dt - timedelta(seconds=1), AAA, NORMAL),
(start_dt, AAA, GAP),
(start_dt.replace(fold=1), BBB, GAP),
(start_dt + ONE_H, BBB, NORMAL),
(end_dt - ONE_H - timedelta(seconds=1), BBB, NORMAL),
(end_dt - ONE_H, BBB, FOLD),
((end_dt - ONE_H).replace(fold=1), AAA, FOLD),
(end_dt, AAA, NORMAL),
))

@call
def _add():
# Taken from America/Godthab, this rule has a transition on the
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2 changes: 1 addition & 1 deletion Lib/zoneinfo/_zoneinfo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -535,7 +535,7 @@ def year_to_epoch(self, year):
days_before_year = _post_epoch_days_before_year(year)

d = self.d
if self.julian and d >= 59 and calendar.isleap(year):
if self.julian and d >= 60 and calendar.isleap(year):
d += 1

epoch = (days_before_year + d) * 86400
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-10-19-12-00-00.gh-issue-159714.j59fix.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :class:`zoneinfo.ZoneInfo` interpreting the Julian day rule ``J59`` as
February 29 in leap years instead of February 28.
2 changes: 1 addition & 1 deletion Modules/_zoneinfo.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1436,7 +1436,7 @@ dayrule_year_to_timestamp(TransitionRuleType *base_self, int year)
// you would use a Julian day, e.g. J91 always refers to April 1st and J365
// always refers to December 31st.
uint16_t day = self->day;
if (self->julian && day >= 59 && is_leap_year(year)) {
if (self->julian && day >= 60 && is_leap_year(year)) {
day += 1;
}

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