False positive safe-super errors for properties defined in protocol classes using inheritance #14757

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1. nph

   added

   bugmypy got something wrongmypy got something wrong

   on Feb 22, 2023
2. AlexWaygood

   added

   topic-inheritanceInheritance and incompatible overridesInheritance and incompatible overrides

   on Feb 22, 2023
3. paperclipstudio commented on Feb 24, 2023

   

   paperclipstudio

   on Feb 24, 2023

   More actions

   I think I might be able to add to this
   with this code

   from abc import ABC, abstractmethod
   from typing import Any
   
   
   class Interface(ABC):
       @abstractmethod
       def method(self) -> Any:
           pass
   
   
   class Level1_1(Interface):
       def method(self) -> str:
           return ""
   
   
   class Level1_2(Interface):
       def method(self) -> str:
           return ""
   
   
   class Level2(Level1_1, Level1_2):
       def method(self) -> str:
           reveal_type(super(Level1_1, self).method())  # Line 23
           reveal_type(super(Level1_2, self).method())  # Line 24
           super(Level1_1, self).method()
           super(Level1_2, self).method()
           return "TEST"

   We get

   clone.py:23: note: Revealed type is builtins.str
   clone.py:24: note: Revealed type is "Any"
   Success: no issues found in 1 source file^

   Which I believe should both be the builtins.str mypy is not picking up the Level1_2 (I think alway the last class that inherits from Interface) method
4. nph commented on Feb 24, 2023

   

   nph

   on Feb 24, 2023

   Author

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   Thanks @paperclipstudio. I believe mypy is actually correct here. The expression:

   super(Level1_1, self).method()
   

   will call method in Level1_2 - hence the revealed type of str. Whereas the expression:

   super(Level1_2, self).method()
   

   will call method in Interface.
5. paperclipstudio commented on Feb 27, 2023

   

   paperclipstudio

   on Feb 27, 2023

   More actions

   Yes, Sorry my mistake, thanks for the help.
6. ebram96 commented on Nov 8, 2023

   

   ebram96

   on Nov 8, 2023

   Last edited by ebram96

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   I also want to add that this also happens even if we directly call a protocol's method in a class that inherits from that protocol..
   Here's an example that produces the same problem:

   _my_protocol.py

   from typing import Protocol
   
   
   class MyProtocol(Protocol):
       def my_method(self) -> dict[str, int | str]:
           ...
   

   my_mixin.py

   from typing import TYPE_CHECKING
   
   from ._my_protocol import MyProtocol
   
   if TYPE_CHECKING:
       _Base = MyProtocol
   else:
       _Base = object
   
   
   class MyMixin(_Base):
       def my_method(self) -> dict[str, int | str]:
           return super().my_method()
   

   Error:
   error: Call to abstract method "my_method" of "MyProtocol" with trivial body via super() is unsafe [safe-super]
7. nph commented on Nov 9, 2023

   

   nph

   on Nov 9, 2023

   Author

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   Hi @ebram96 - I think mypy is correct in this case. Your MyMixin class is a regular class and not a Protocol class (as it does not explicitly inherit from Protocol itself) and since MyProtocol does not provide an implementation of my_method, mypy is correct to raise a safe-super error for the super().my_method() call. PEP544 gives a similar example of a safe-super error for the BadColor class.
8. jace commented on Jun 28, 2024

   

   jace

   on Jun 28, 2024

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   I have a variant of this error for a mixin class using super() against a protocol:

   from typing import Protocol
   
   
   class BaseClassProtocol(Protocol):
       def some_method(self) -> str | None: ...
   
   
   class SubClassProtocol(BaseClassProtocol, Protocol):
       @property
       def some_flag(self) -> str: ...
   
   
   class MyMixin:
       def some_method(self: SubClassProtocol) -> str | None:
           if self.some_flag:  # `self` type is defined to access this
               return 'some_flag'
           return super().some_method()  # But this is flagged for `safe_super`

   Playground URL: https://mypy-play.net/?mypy=latest&python=3.12&gist=7129a6792261d89c8e3b414a6f12e0f8
9. jace commented on Jun 28, 2024

   

   jace

   on Jun 28, 2024

   More actions

   The fix from #12344 / #14082 doesn't work to stop the safe_super error, but replacing the method definition with Callable type makes the error go away:

   from collections.abc import Callable
   from typing import Protocol
   
   class MixinProtocol(Protocol):
       some_method: Callable
   
       @property
       def some_flag(self) -> str: ...
   
   class MyMixin:
       def some_method(self: MixinProtocol) -> str | None:
           if self.some_flag:
               return 'some_flag'
           return super().some_method()  # No error now!
10. khaeru

    added a commit that references this issue on Aug 9, 2024

    Satisfy mypy 1.11.1

    ...

    65a807f