Incompatible definition between base classes

[squiddy]

Sorry for the rather vague title, but I can't put it more precise. Find below a code example, I tried to keep it relevant for my use case. Note that, while the code shown is python3, the actual usage is in python2. Both versions behave identical though.

class Window:
    """
    Base class for all elements that act like windows, can be shown and hidden.
    """
    def show(self, **kwargs):
        # this is supposed to be implemented by subclasses
        raise NotImplementedError


class SpecialWidget:
    """
    Widget that shows things, like a table that is updated.
    """
    def show(self):
        # setup gui elements
        pass

    def update_things(self):
        pass


class FooWindow(SpecialWidget, Window): # <-- E: Definition of "show" in base class "SpecialWidget" is incompatible with definition in base class "Window"
    """
    A window that uses the GUI setup of SpecialWidget.
    """
    def update_things(self):
        pass

I fully understand the error, however, I'm at a loss on what to do about it. Obviously I could add **kwargs to Specialwidget.show, that gets rid of the error. But I don't really want to do that.

I tried to add my own show implementation in FooWindow:

    def show(self):
        SpecialWidget.show(self)

But that doesn't work. I also tried to have mypy ignore the definitions:

    def show(self): # type: ignore
        # setup gui elements
        pass

But that doesn't seem to be working either.

I'd appreciate any pointers, be it help with ignoring the error, fixing it or refactoring the code to avoid this issue.

[gvanrossum]

I think this is a dupe of #1237. But I'm surprised the # type: ignore doesn't work.

[JukkaL]

This gets rid of the error for me (the comment needs to be on the line where the error is reported):

class FooWindow(SpecialWidget, Window): # type: ignore

Closing this issue for now; feel free to reopen is this still doesn't address your issue.