提供一個共同的介面來建立相互關聯的多個物件。

抽象工廠模式的用意為：給客戶端提供一個介面，可以建立多個產品族中的產品物件。 不過使用抽象工廠是有條件的：
1.系統中有多個產品族，而系統一次只可能消費其中一族產品

2.同屬於同一個產品族的產品在一起使用，這一約束必須在系統的設計中體現出來。

定義兩個類，Dog和Cat，都擁有speak方法

class Dog(object):

    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"


class Cat(object):

    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"
 

寫一個抽象工廠類PetShop.

class PetShop(object):

    """A pet shop"""

    def __init__(self, animal_factory=None):
        """pet_factory is our abstract factory.  We can set it at will."""

        self.pet_factory = animal_factory

    def show_pet(self):
        """Creates and shows a pet using the abstract factory"""

        pet = self.pet_factory()
        print("We have a lovely {}".format(pet))
        print("It says {}".format(pet.speak()))
 

初始化時，傳一個Dog 或者 Cat，之後就跟普通的呼叫是一樣的。show_pet中，初始化傳入的類。

    cat_shop = PetShop(Cat)
    cat_shop.show_pet()

完整程式碼如下：

import random


class PetShop(object):

    """A pet shop"""

    def __init__(self, animal_factory=None):
        """pet_factory is our abstract factory.  We can set it at will."""

        self.pet_factory = animal_factory

    def show_pet(self):
        """Creates and shows a pet using the abstract factory"""

        pet = self.pet_factory()
        print("We have a lovely {}".format(pet))
        print("It says {}".format(pet.speak()))


class Dog(object):

    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"


class Cat(object):

    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"


# Additional factories:

# Create a random animal
def random_animal():
    """Let's be dynamic!"""
    return random.choice([Dog, Cat])()


# Show pets with various factories
if __name__ == "__main__":

    # A Shop that sells only cats
    cat_shop = PetShop(Cat)
    cat_shop.show_pet()
    print("")

    # A shop that sells random animals
    shop = PetShop(random_animal)
    for i in range(3):
        shop.show_pet()
        print("=" * 20)