container.py

# -*- coding: utf-8 -*-

# from sig import Provider


class Container(dict):

    def __delitem__(self, name):
        if self.has(name):
            dict.__delitem__(self, name)

    def has(self, name):
        return name in self

    # def register(self, provider: Container):
    def register(self, provider):
        provider.register(self)

# does not work
if __name__ == '__main__':
    container = Container()
    container.register(TestProvider())

provider.py

# -*- coding: utf-8 -*-

from abc import ABCMeta, abstractmethod
from sig import Container


class Provider(metaclass=ABCMeta):

    @abstractmethod
    def register(self, container: Container):
        pass

@sergiors como está chamando o método register? Provider.register() ou Provider().register()

A ideia é fazer algo semelhante ao código abaixo:

container = Container()
container.register(TestProvider())

dai o container passa ela para o provider