Get PyCharm to know what classes are mixin for

Question

Our application has set of complex form wizards. To avoid code duplication I created several mixins.

The problem is that PyCharm highlights mixin methods with Unre

Answer 1

If you are creating Mixin, for, let's say ClassSub, which is subclass of ClassSuper, you can implement Mixins this way:

class Mixin1(ClassSuper):
    pass


class Mixin2(ClassSuper):
    pass

and then use them like:

class ClassSub(Mixin1, Mixin2):
    pass

That way I use some mixins for models in Django. Also, django-extensions uses similar pattern (gives models that are actually mixins). Basically, this way you don't have to inherit ClassSuper, because it's "included" in every of your mixins.

Most important - PyCharm works like a charm this way.

Answer 2

You can type-hint to PyCharm what kind of classes to expect.

class DictMixin(object):
    def megamethod(
        self,  # type: dict
        key
    ):
        return self.get(key)

It's still not quite comparable to other type handling. PyCharm is lazy in evaluating it, and only does so when first working on self. Things are a bit tricky when accessing attributes of the mixin as well - self, # type: dict | DictMixin works for one of my classes, but not in my test code. In python 3.5, you should be able to use # type: typing.Union[dict, DictMixin].