bridge.py

from abc import ABC, abstractmethod


# Abstract Interface (aka Handle) used by the client
class Website(ABC):
    def __init__(self, implementation):
        # encapsulate an instance of a concrete implementation class
        self._implementation = implementation

    def __str__(self):
        return "Interface: {}; Implementation: {}".format(
            self.__class__.__name__, self._implementation.__class__.__name__
        )

    @abstractmethod
    def show_page(self):
        pass


# Concrete Interface 1
class FreeWebsite(Website):
    def show_page(self):
        ads = self._implementation.get_ads()
        text = self._implementation.get_excerpt()
        call_to_action = self._implementation.get_call_to_action()
        print(ads)
        print(text)
        print(call_to_action)
        print("")


# Concrete Interface 2
class PaidWebsite(Website):
    def show_page(self):
        text = self._implementation.get_article()
        print(text)
        print("")


# Abstract Implementation (aka Body) decoupled from the client
class Implementation(ABC):
    def get_excerpt(self):
        return "excerpt from the article"

    def get_article(self):
        return "full article"

    def get_ads(self):
        return "some ads"

    @abstractmethod
    def get_call_to_action(self):
        pass


# Concrete Implementation 1
class ImplementationA(Implementation):
    def get_call_to_action(self):
        return "Pay 10 $ a month to remove ads"


# Concrete Implementation 2
class ImplementationB(Implementation):
    def get_call_to_action(self):
        return "Remove ads with just 10 $ a month"


# Client
def main():
    a_free = FreeWebsite(ImplementationA())
    print(a_free)
    a_free.show_page()  # the client interacts only with the interface

    b_free = FreeWebsite(ImplementationB())
    print(b_free)
    b_free.show_page()

    a_paid = PaidWebsite(ImplementationA())
    print(a_paid)
    a_paid.show_page()

    b_paid = PaidWebsite(ImplementationB())
    print(b_paid)
    b_paid.show_page()


if __name__ == "__main__":
    main()