Scenario

I have a Foo protocol:

class Foo(Protocol):
    fooname: str

    def do_fooey_things(self):
        pass

and a bunch of different types of concrete Foos:

class PurpleFoo:
    fooname: str = "purple"

    def do_fooey_things(self):
        print("purple foo!")

What I’ve achieved with this is a way of being able to type-hint, have my IDE help me, and run tests to make sure all my concrete Foos are doing what I expect: isinstance(purple_foo, Foo). And I’ve met another design requirement which is I want to minimize abstraction (ie I don’t want to use abstract base classes).

But now I need all my Foo’s to use a mixin from a third party library like:

class PurpleFoo(BarMixin):
    ....

But now my IDE can’t help me with the BarMixin methods and attributes, and my isinstance checks will pass even if one of the Foos fails to use BarMixin (and I want them all too use it).

Question and what I’ve tried

I know I can’t do

class Foo(Protocol, BarMixin)
    ...

So what do I do?

The best I’ve come up with so far is to make Foo have class attributes pointing to the attributes and methods of BarMixin that I’m interested in adopting:

class Foo(Protocol, BarMixin)
    fooname: str
    bar_attribute = BarMixin.bar_attribute
    bar_method = BarMixin.bar_method

At least this way I benefit from the IDE help (at least in VSCode) and the isinstance check catches any Foo’s that don’t inherit from BarMixin.