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GH-93521: Filter out __weakref__ slot if present in bases #93535

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Merged
merged 4 commits into from
Jun 8, 2022
Merged

GH-93521: Filter out __weakref__ slot if present in bases #93535

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abdab30
GH-93521: Filter out `__weakref__` slot if present in bases
Bluenix2 Jun 6, 2022
5ee1d76
📜🤖 Added by blurb_it.
blurb-it[bot] Jun 6, 2022
47a107f
Expand test coverage of subclasses specifying `__weakref__`
Bluenix2 Jun 6, 2022
187a0fe
Reword news blurb to explain change without context
Bluenix2 Jun 6, 2022
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13 changes: 9 additions & 4 deletions Lib/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1156,11 +1156,16 @@ def _add_slots(cls, is_frozen, weakref_slot):
itertools.chain.from_iterable(map(_get_slots, cls.__mro__[1:-1]))
)
# The slots for our class. Remove slots from our base classes. Add
# '__weakref__' if weakref_slot was given.
# '__weakref__' if weakref_slot was given, unless it is already present.
cls_dict["__slots__"] = tuple(
itertools.chain(
itertools.filterfalse(inherited_slots.__contains__, field_names),
("__weakref__",) if weakref_slot else ())
itertools.filterfalse(
inherited_slots.__contains__,
itertools.chain(
# gh-93521: '__weakref__' also needs to be filtered out if
# already present in inherited_slots
field_names, ('__weakref__',) if weakref_slot else ()
)
),
)

for field_name in field_names:
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16 changes: 16 additions & 0 deletions Lib/test/test_dataclasses.py
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Expand Up @@ -3109,6 +3109,22 @@ def test_weakref_slot_make_dataclass(self):
"weakref_slot is True but slots is False"):
B = make_dataclass('B', [('a', int),], weakref_slot=True)

def test_weakref_slot_subclass_also_weakref_slot(self):
@dataclass(slots=True, weakref_slot=True)
class Base:
field: int

# A *can* also specify weakref_slot=True if it wants to (gh-93521)
@dataclass(slots=True, weakref_slot=True)
class A(Base):
...

# __weakref__ is in the base class, not A. But an instance of A
# is still weakref-able.
self.assertIn("__weakref__", Base.__slots__)
self.assertNotIn("__weakref__", A.__slots__)
a = A(1)
weakref.ref(a)

class TestDescriptors(unittest.TestCase):
def test_set_name(self):
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-06-06-13-19-43.gh-issue-93521._vE8m9.rst
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@@ -0,0 +1 @@
Allow specifying ``weakref_slot`` several times in dataclass MRO