10000 Loosen base class attribute compatibility checks when attribute is redefined by syastrov · Pull Request #6585 · python/mypy · GitHub
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Loosen base class attribute compatibility checks when attribute is redefined #6585

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Merged
merged 4 commits into from
Apr 12, 2019
Merged

Loosen base class attribute compatibility checks when attribute is redefined #6585

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8e20acc
Loosen base class attribute compatibility checks when attribute is re…
syastrov Mar 24, 2019
8adafdb
Remove extra newlines.
syastrov Apr 10, 2019
3a38d4b
Restore the current behavior regarding incompatible type in assignment.
syastrov Apr 11, 2019
e807d81
Style fixes
ilevkivskyi Apr 12, 2019
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Remove extra newlines.
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@syastrov
syastrov committed Apr 10, 2019
commit 8adafdb664946e296c33739fca0bb56b9657e085
1 change: 0 additions & 1 deletion test-data/unit/check-classes.test
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Expand Up @@ -4020,7 +4020,6 @@ class C(B):
[out]
main:6: error: Incompatible types in assignment (expression has type "str", base class "A" defined the type as "int")
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Same as above. A user might want to ignore the error once in the base class, instead of ignoring it in every subclass.

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This is slightly different than the above situation, as here, there was no error before.

I think it depends on how you want to interpret the # type: ignore.
In the current behavior, because B.x has an ignore, you are no longer warned when you redefine x in C.x that that redefinition is actually incompatible with ancestor's A.x.

A library author may have defined B.x with the ignore comment, and let us say that you are writing class C yourself. I would find it unexpected that because the library author chose to add an ignore comment on B.x that that would suppress a certain type of error when defining my own class.
I may not know in detail how B is defined/type-annotated, so I may reasonably expect that the type checker would perform its normal checks for my definition of class C (in this case, that it is compatible with A).

Are there other places in mypy where # type: ignore comments "spread" in that sense?

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Oops:
(in this case, that it is compatible with A)
should be:
(in this case, that C.x is actually compatible with A.x)

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Are there other places in mypy where # type: ignore comments "spread" in that sense?

Practically everywhere, an invalid type, a failed attribute access, an operator, or sometimes even failed function call, produce an Any type thus preventing subsequent errors.



[case testClassIgnoreType_RedefinedAttributeTypeIgnoredInChildren]
class A:
x = 0
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11 changes: 2 additions & 9 deletions test-data/unit/check-multiple-inheritance.test
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Expand Up @@ -462,7 +462,6 @@ class Combo(Base2, Base1): ...
main:10: error: Definition of "NestedVar" in base class "Base2" is incompatible with definition in base class "Base1"

[case testMultipleInheritance_NestedVariableOverriddenWithCompatibleType]

from typing import TypeVar, Generic
T = TypeVar('T', covariant=True)
class GenericBase(Generic[T]):
Expand All @@ -476,7 +475,6 @@ class A(Base1, Base2):
[out]

[case testMultipleInheritance_NestedVariableOverriddenWithIncompatibleType1]

from typing import TypeVar, Generic
T = TypeVar('T', covariant=True)
class GenericBase(Generic[T]):
Expand All @@ -488,10 +486,9 @@ class Base2:
class A(Base1, Base2):
Nested: GenericBase['Base1']
[out]
main:11: error: Incompatible types in assignment (expression has type "GenericBase[Base1]", base class "Base2" defined the type as "GenericBase[Base2]")
main:10: error: Incompatible types in assignment (expression has type "GenericBase[Base1]", base class "Base2" defined the type as "GenericBase[Base2]")

[case testMultipleInheritance_NestedVariableOverriddenWithIncompatibleType2]

from typing import TypeVar, Generic
T = TypeVar('T', covariant=True)
class GenericBase(Generic[T]):
Expand All @@ -503,11 +500,9 @@ class Base2:
class A(Base1, Base2):
Nested: GenericBase['Base2']
[out]
main:11: error: Incompatible types in assignment (expression has type "GenericBase[Base2]", base class "Base1" defined the type as "GenericBase[Base1]")

main:10: error: Incompatible types in assignment (expression has type "GenericBase[Base2]", base class "Base1" defined the type as "GenericBase[Base1]")

[case testMultipleInheritance_NestedVariableOverriddenWithCompatibleType]

from typing import TypeVar, Generic
T = TypeVar('T', covariant=True)
class GenericBase(Generic[T]):
Expand All @@ -520,8 +515,6 @@ class A(Base1, Base2):
Nested: GenericBase['Base1']
[out]



[case testMultipleInheritance_MethodDefinitionsCompatibleWithOverride]
from typing import TypeVar, Union
_T = TypeVar('_T')
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