Alternatively, the need for an overriding implementation to call super could be marked by a different decorator.  This would allow linters to check that subclasses call super when they should, which is a very useful check in my opinion.  Such a decorator could be called "@overrideable", and could be exposed in abc.   When used in combination with @abstractmethod, it could have the above behavior. 

On Sunday, February 17, 2019 at 5:28:49 AM UTC-5, Neil Girdhar wrote:
Marking a method M declared in C with abstractmethod indicates that M needs to be *implemented* in any subclass D of C for D to be instantiated.

We usually think of overriding a method N to mean replacing one implementation in some class E with another in some subclass of E, F.  Often, the subclass implementation calls super to add behavior rather than replace it.

I think that this concept of *implementing* is different than *overriding*.

However, abstract classes can have reasonable definition, and should sometimes be overridden in the sense that subclasses should call super.  For example, when inheriting from AbstractContextManager, you need to *override* the abstractmethod (!) __exit__, and if you want your class to work polymorphically, you should call super.

This is extremely weird.  Understandably, the pylint people are confused by it (https://github.com/PyCQA/pylint/issues/1594) and raise bad warnings.

It also makes it impossible for me to raise warnings in my ipromise (https://github.com/NeilGirdhar/ipromise) project.  See, for example, https://github.com/NeilGirdhar/ipromise/blob/master/ipromise/test/test_overrides.py classes Y and W, which ought to raise, but that would raise on reasonable code.

My suggestion is to add a rarely used flag to abstractmethod:

class AbstractContextManager:
    @abstractmethod(overrideable=True)
    def __exit__(self, exc_type, exc_value, traceback):
        pass

This would set a flag on the method like __abstractmethod_overrideable__, which could be checked by ipromise's @overrides decorator, pylint's call check, and anyone else that wants to know that a method should be overridden.

Best,

Neil