Do I need to provide type hints for methods overriding `@abstractmethod`s?

Question

Given these two classes:

class MyClass(ABC):
    @abstractmethod
    def my_method(self, my_parameter: str):
        pass
    
class MySecondClass(MyClass):
    def my_method(self, my_parameter): 
        pass

Does my_parameter in my_method of MySecondClass have an inferred type of Any or str based on PEP 484? I couldn't find an example detailing the above within the linked document.

Answer 1

It's Any. You can try it out by running mypy:

from abc import ABC, abstractmethod

class MyClass(ABC):
    @abstractmethod
    def my_method(self, my_parameter: str):
        pass
    
class MySecondClass(MyClass):
    def my_method(self, my_parameter):
        reveal_type(my_parameter)
        pass

MySecondClass().my_method(3)

With or without the --check-untyped-defs flag, this passes type checking, and reveal_type reports Any as the type. (Without the flag, type checking is also skipped for the method body.)

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Note that even with annotations, it is permitted for an overriding method to have a different signature than an overridden method, as long as the overriding method's signature is more permissive. For example, a method that takes an Animal can override a method that takes a Dog.