GH-90750: Use datetime.fromisocalendar in _strptime (#103802)
Use datetime.fromisocalendar in _strptime
This unifies the ISO → Gregorian conversion logic and improves handling
of invalid ISO weeks.
diff --git a/Lib/_strptime.py b/Lib/_strptime.py
index b97dfcc..77ccdc9 100644
--- a/Lib/_strptime.py
+++ b/Lib/_strptime.py
@@ -290,22 +290,6 @@ def _calc_julian_from_U_or_W(year, week_of_year, day_of_week, week_starts_Mon):
return 1 + days_to_week + day_of_week
-def _calc_julian_from_V(iso_year, iso_week, iso_weekday):
- """Calculate the Julian day based on the ISO 8601 year, week, and weekday.
- ISO weeks start on Mondays, with week 01 being the week containing 4 Jan.
- ISO week days range from 1 (Monday) to 7 (Sunday).
- """
- correction = datetime_date(iso_year, 1, 4).isoweekday() + 3
- ordinal = (iso_week * 7) + iso_weekday - correction
- # ordinal may be negative or 0 now, which means the date is in the previous
- # calendar year
- if ordinal < 1:
- ordinal += datetime_date(iso_year, 1, 1).toordinal()
- iso_year -= 1
- ordinal -= datetime_date(iso_year, 1, 1).toordinal()
- return iso_year, ordinal
-
-
def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
"""Return a 2-tuple consisting of a time struct and an int containing
the number of microseconds based on the input string and the
@@ -483,7 +467,8 @@ def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
else:
tz = value
break
- # Deal with the cases where ambiguities arize
+
+ # Deal with the cases where ambiguities arise
# don't assume default values for ISO week/year
if year is None and iso_year is not None:
if iso_week is None or weekday is None:
@@ -511,7 +496,6 @@ def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
elif year is None:
year = 1900
-
# If we know the week of the year and what day of that week, we can figure
# out the Julian day of the year.
if julian is None and weekday is not None:
@@ -520,7 +504,10 @@ def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
julian = _calc_julian_from_U_or_W(year, week_of_year, weekday,
week_starts_Mon)
elif iso_year is not None and iso_week is not None:
- year, julian = _calc_julian_from_V(iso_year, iso_week, weekday + 1)
+ datetime_result = datetime_date.fromisocalendar(iso_year, iso_week, weekday + 1)
+ year = datetime_result.year
+ month = datetime_result.month
+ day = datetime_result.day
if julian is not None and julian <= 0:
year -= 1
yday = 366 if calendar.isleap(year) else 365
diff --git a/Lib/test/test_strptime.py b/Lib/test/test_strptime.py
index e3fcabe..810c5a3 100644
--- a/Lib/test/test_strptime.py
+++ b/Lib/test/test_strptime.py
@@ -242,6 +242,16 @@ def test_ValueError(self):
# 5. Julian/ordinal day (%j) is specified with %G, but not %Y
with self.assertRaises(ValueError):
_strptime._strptime("1999 256", "%G %j")
+ # 6. Invalid ISO weeks
+ invalid_iso_weeks = [
+ "2019-00-1",
+ "2019-54-1",
+ "2021-53-1",
+ ]
+ for invalid_iso_dtstr in invalid_iso_weeks:
+ with self.subTest(invalid_iso_dtstr):
+ with self.assertRaises(ValueError):
+ _strptime._strptime(invalid_iso_dtstr, "%G-%V-%u")
def test_strptime_exception_context(self):
diff --git a/Misc/NEWS.d/next/Library/2023-04-24-16-00-28.gh-issue-90750.da0Xi8.rst b/Misc/NEWS.d/next/Library/2023-04-24-16-00-28.gh-issue-90750.da0Xi8.rst
new file mode 100644
index 0000000..99e10f1
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-04-24-16-00-28.gh-issue-90750.da0Xi8.rst
@@ -0,0 +1,3 @@
+Use :meth:`datetime.datetime.fromisocalendar` in the implementation of
+:meth:`datetime.datetime.strptime`, which should now accept only valid ISO
+dates. (Patch by Paul Ganssle)
