structural/adapter.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
*What is this pattern about?
The Adapter pattern provides a different interface for a class. We can
think about it as a cable adapter that allows you to charge a phone
somewhere that has outlets in a different shape. Following this idea,
the Adapter pattern is useful to integrate classes that couldn't be
integrated due to their incompatible interfaces.

*What does this example do?

The example has classes that represent entities (Dog, Cat, Human, Car)
that make different noises. The Adapter class provides a different
interface to the original methods that make such noises. So the
original interfaces (e.g., bark and meow) are available under a
different name: make_noise.

*Where is the pattern used practically?
The Grok framework uses adapters to make objects work with a
particular API without modifying the objects themselves:
http://grok.zope.org/doc/current/grok_overview.html#adapters

*References:
http://ginstrom.com/scribbles/2008/11/06/generic-adapter-class-in-python/
https://sourcemaking.com/design_patterns/adapter
http://python-3-patterns-idioms-test.readthedocs.io/en/latest/ChangeInterface.html#adapter

*TL;DR80
Allows the interface of an existing class to be used as another interface.
"""


class Dog(object):

    def __init__(self):
        self.name = "Dog"

    def bark(self):
        return "woof!"


class Cat(object):

    def __init__(self):
        self.name = "Cat"

    def meow(self):
        return "meow!"


class Human(object):

    def __init__(self):
        self.name = "Human"

    def speak(self):
        return "'hello'"


class Car(object):

    def __init__(self):
        self.name = "Car"

    def make_noise(self, octane_level):
        return "vroom{0}".format("!" * octane_level)


class Adapter(object):
    """
    Adapts an object by replacing methods.
    Usage:
    dog = Dog()
    dog = Adapter(dog, make_noise=dog.bark)

    >>> objects = []
    >>> dog = Dog()
    >>> print(dog.__dict__)
    {'name': 'Dog'}
    >>> objects.append(Adapter(dog, make_noise=dog.bark))
    >>> print(objects[0].original_dict())
    {'name': 'Dog'}
    >>> cat = Cat()
    >>> objects.append(Adapter(cat, make_noise=cat.meow))
    >>> human = Human()
    >>> objects.append(Adapter(human, make_noise=human.speak))
    >>> car = Car()
    >>> car_noise = lambda: car.make_noise(3)
    >>> objects.append(Adapter(car, make_noise=car_noise))

    >>> for obj in objects:
    ...     print('A {} goes {}'.format(obj.name, obj.make_noise()))
    A Dog goes woof!
    A Cat goes meow!
    A Human goes 'hello'
    A Car goes vroom!!!
    """

    def __init__(self, obj, **adapted_methods):
        """We set the adapted methods in the object's dict"""
        self.obj = obj
        self.__dict__.update(adapted_methods)

    def __getattr__(self, attr):
        """All non-adapted calls are passed to the object"""
        return getattr(self.obj, attr)

    def original_dict(self):
        """Print original object dict"""
        return self.obj.__dict__

def main():

    objects = []
    dog = Dog()
    print(dog.__dict__)
    objects.append(Adapter(dog, make_noise=dog.bark))
    print(objects[0].__dict__)
    print(objects[0].original_dict())
    cat = Cat()
    objects.append(Adapter(cat, make_noise=cat.meow))
    human = Human()
    objects.append(Adapter(human, make_noise=human.speak))
    car = Car()
    objects.append(Adapter(car, make_noise=lambda: car.make_noise(3)))

    for obj in objects:
        print("A {0} goes {1}".format(obj.name, obj.make_noise()))


if __name__ == "__main__":
    main()

### OUTPUT ###
# {'name': 'Dog'}
# {'make_noise': <bound method Dog.bark of <__main__.Dog object at 0x7f631ba3fb00>>, 'obj': <__main__.Dog object at 0x7f631ba3fb00>}
# {'name': 'Dog'}
# A Dog goes woof!
# A Cat goes meow!
# A Human goes 'hello'
# A Car goes vroom!!!