Method test_fold_mutate

Lib/test/test_zoneinfo/test_zoneinfo.py:452–500

Test that fold isn't mutated when no change is necessary. The underlying C API is capable of mutating datetime objects, and may rely on the fact that addition of a datetime object returns a new datetime; this test ensures that the input datetime to fromutc is not mut

(self)

                inspect.Signature.from_callable(method)

    def test_fold_mutate(self):
        """Test that fold isn't mutated when no change is necessary.

        The underlying C API is capable of mutating datetime objects, and
        may rely on the fact that addition of a datetime object returns a
        new datetime; this test ensures that the input datetime to fromutc
        is not mutated.
        """

        def to_subclass(dt):
            class SameAddSubclass(type(dt)):
                def __add__(self, other):
                    if other == timedelta(0):
                        return self

                    return super().__add__(other)  # pragma: nocover

            return SameAddSubclass(
                dt.year,
                dt.month,
                dt.day,
                dt.hour,
                dt.minute,
                dt.second,
                dt.microsecond,
                fold=dt.fold,
                tzinfo=dt.tzinfo,
            )

        subclass = [False, True]

        key = "Europe/London"
        zi = self.zone_from_key(key)
        for zt in self.load_transition_examples(key):
            if zt.fold and zt.offset_after.utcoffset == ZERO:
                example = zt.transition_utc.replace(tzinfo=zi)
                break

        for subclass in [False, True]:
            if subclass:
                dt = to_subclass(example)
            else:
                dt = example

            with self.subTest(subclass=subclass):
                dt_fromutc = zi.fromutc(dt)

                self.assertEqual(dt_fromutc.fold, 1)
                self.assertEqual(dt.fold, 0)


class ZoneInfoDatetimeSubclassTest(DatetimeSubclassMixin, ZoneInfoTest):