Python Mixin - Unresolved Attribute Reference [PyCharm]

Declare the necessary fields in the Mixin like:

class Mixin:    foo: str    def complex_operation(self):        return self.foo.capitalize() 

This way the mixin actually declares the fields a class must have to be able to use this mixin. Type hint will create warnings if extending class will put incompatible type into declared field.

edit: Replaced foo = None with foo:str as suggested by @valex

I see few options.

1) Type annotations (i think this is cleanest solution):

class Mixin:    foo: str    def complex_operation(self):        return self.foo.capitalize()

2) Default None (@ikamen option):

class Mixin:    foo = None    def complex_operation(self):        return self.foo.capitalize()

3) Suppress unresolved reference error for class or for specific line (i think this is more dirty way than first two):

# noinspection PyUnresolvedReferencesclass Mixin:    def complex_operation(self):        return self.foo.capitalize()

class Mixin:    def complex_operation(self):        # noinspection PyUnresolvedReferences        return self.foo.capitalize()

So just to compiling my thoughts from the comments for everyone else: The problem is keeping the two classes intrinsically connected while separating functionality. Here are my solutions:

1) Make a module

Have another file, say mixin.py, that has complex_operation as a function. Instead of accepting self as a parameter, have it take a string:

# mixin.pydef complex_operation (foo: str) -> str: return foo.capitalize()# main.pyfrom ai import complex_operationclass A:     def __init__(self): self.foo = "foo"print (complex_operation (A().foo))

2) Make a class to accept another class as a parameter

In Mixin's __init__ function, add a parameter to accept an A, and then use that in its methods:

# mixin.pyclass Mixin:     def __init__(self, a: A): self.a = a    def complex_operation(self): return self.a.foo.capitalize()# main.pyfrom mixin import Mixinclass A:    def __init__(self): self.foo = "foo"print (Mixin (A()).complex_operation())