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[3.13] gh-152060: Fix _pydatetime.fromisoformat() raising AssertionError on invalid lengths (GH-152061) #152787

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Merged
StanFromIreland merged 3 commits into from
Jul 1, 2026
Merged

[3.13] gh-152060: Fix _pydatetime.fromisoformat() raising AssertionError on invalid lengths (GH-152061) #152787

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gh-152060: Fix `_pydatetime.fromisoformat()` raising `AssertionError`…
tonghuaroot Jul 1, 2026
4ebd407
Fix comment
StanFromIreland Jul 1, 2026
3b86c17
oops one more space
StanFromIreland Jul 1, 2026
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3 changes: 2 additions & 1 deletion Lib/_pydatetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -335,7 +335,8 @@ def _find_isoformat_datetime_separator(dtstr):
def _parse_isoformat_date(dtstr):
# It is assumed that this is an ASCII-only string of lengths 7, 8 or 10,
# see the comment on Modules/_datetimemodule.c:_find_isoformat_datetime_separator
assert len(dtstr) in (7, 8, 10)
if len(dtstr) not in (7, 8, 10):
raise ValueError("Invalid isoformat string")
year = int(dtstr[0:4])
has_sep = dtstr[4] == '-'

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1 change: 1 addition & 0 deletions Lib/test/datetimetester.py
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Expand Up @@ -3395,6 +3395,7 @@ def test_fromisoformat_fails_datetime(self):
'2009-04-19T12:30:45.400 +02:30', # Space between ms and timezone (gh-130959)
'2009-04-19T12:30:45.400 ', # Trailing space (gh-130959)
'2009-04-19T12:30:45. 400', # Space before fraction (gh-130959)
'2020-2020', # Ambiguous 9-char date portion
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]

for bad_str in bad_strs:
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-24-10-46-35.gh-issue-152060.f2asrt.rst
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@@ -0,0 +1,3 @@
Fix :meth:`datetime.datetime.fromisoformat` raising :exc:`AssertionError`
instead of :exc:`ValueError` for some malformed strings in the pure-Python
implementation, matching the C implementation.
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