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Allow incompatible overriding of __slots__ #4890

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Merged
merged 2 commits into from
Apr 13, 2018
Merged

Allow incompatible overriding of __slots__ #4890

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6b17222
Allow incompatible overriding of __slots__
JukkaL Apr 12, 2018
36bae9f
Test invalid __slots__ value
JukkaL Apr 13, 2018
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3 changes: 3 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1390,6 +1390,9 @@ def check_compatibility(self, name: str, base1: TypeInfo,
if second_type is None:
self.msg.cannot_determine_type_in_base(name, base2.name(), ctx)
ok = True
# __slots__ is special and the type can vary across class hierarchy.
if name == '__slots__':
ok = True
if not ok:
self.msg.base_class_definitions_incompatible(name, base1, base2,
ctx)
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13 changes: 13 additions & 0 deletions test-data/unit/check-classes.test
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Expand Up @@ -4186,6 +4186,9 @@ class F(six.with_metaclass(t.M)): pass
@six.add_metaclass(t.M)
class G: pass

-- Misc
-- ----

[case testCorrectEnclosingClassPushedInDeferred]
class C:
def __getattr__(self, attr: str) -> int:
Expand Down Expand Up @@ -4296,3 +4299,13 @@ class C: pass

@undefined # E: Name 'undefined' is not defined
class D: pass

[case testSlotsCompatibility]
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Should we test that there is still an error if we set __slots__ to something nonsensical like an int?

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Added a test case.

class A:
__slots__ = ()
class B(A):
__slots__ = ('a', 'b')
class C:
__slots__ = ('x',)
class D(B, C):
__slots__ = ('aa', 'bb', 'cc')
9 changes: 9 additions & 0 deletions test-data/unit/pythoneval.test
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Expand Up @@ -1250,3 +1250,12 @@ def g(si: Iterable[str]):
pass
f(E)
g(E)

[case testInvalidSlots]
class A:
__slots__ = 1
class B:
__slots__ = (1, 2)
[out]
_testInvalidSlots.py:2: error: Incompatible types in assignment (expression has type "int", base class "object" defined the type as "Union[str, Iterable[str], None]")
_testInvalidSlots.py:4: error: Incompatible types in assignment (expression has type "Tuple[int, int]", base class "object" defined the type as "Union[str, Iterable[str], None]")