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Merge pull request faif#215 from spookylukey/pythonic_abstract_factory
Simplified the Abstract Factory Pattern to be Pythonic
2 parents ac79516 + 6127f9d commit 5e05ca1

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‎creational/abstract_factory.py‎

Lines changed: 28 additions & 73 deletions
Original file line numberDiff line numberDiff line change
@@ -3,22 +3,25 @@
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"""
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*What is this pattern about?
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The Abstract Factory Pattern serves to provide an interface for
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In Java and other languages, the Abstract Factory Pattern serves to provide an interface for
78
creating related/dependent objects without need to specify their
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actual class.
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The idea is to abstract the creation of objects depending on business
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logic, platform choice, etc.
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In Python, we interface we use is simply a callable, which is "builtin" interface
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in Python, and in normal circumstances we can simply use the class itself as
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that callable, because classes are first class objects in Python.
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*What does this example do?
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This particular implementation abstracts the creation of a pet and
14-
does so depending on the AnimalFactory we chose (Dog or Cat)
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This works because both Dog/Cat and their factories respect a common
16-
interface (.speak(), get_pet() and get_food()).
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Now my application can create pets (and feed them) abstractly and decide later,
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does so depending on the factory we chose (Dog or Cat, or random_animal)
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This works because both Dog/Cat and random_animal respect a common
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interface (callable for creation and .speak()).
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Now my application can create pets abstractly and decide later,
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based on my own criteria, dogs over cats.
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The second example allows us to create pets based on the string passed by the
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user, using cls.__subclasses__ (the list of sub classes for class cls)
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and sub_cls.__name__ to get its name.
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*Where is the pattern used practically?
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@@ -30,9 +33,6 @@
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Provides a way to encapsulate a group of individual factories.
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"""
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import six
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import abc
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import random
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@@ -48,14 +48,11 @@ def __init__(self, animal_factory=None):
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def show_pet(self):
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"""Creates and shows a pet using the abstract factory"""
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51-
pet = self.pet_factory.get_pet()
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pet = self.pet_factory()
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print("We have a lovely {}".format(pet))
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print("It says {}".format(pet.speak()))
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print("We also have {}".format(self.pet_factory.get_food()))
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5655

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# Stuff that our factory makes
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5956
class Dog(object):
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6158
def speak(self):
@@ -74,80 +71,38 @@ def __str__(self):
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return "Cat"
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# Factory classes
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class DogFactory(object):
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def get_pet(self):
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return Dog()
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def get_food(self):
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return "dog food"
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# Additional factories:
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class CatFactory(object):
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def get_pet(self):
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return Cat()
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def get_food(self):
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return "cat food"
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# Create the proper family
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def get_factory():
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# Create a random animal
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def random_animal():
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"""Let's be dynamic!"""
100-
return random.choice([DogFactory, CatFactory])()
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# Implementation 2 of an abstract factory
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@six.add_metaclass(abc.ABCMeta)
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class Pet(object):
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@classmethod
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def from_name(cls, name):
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for sub_cls in cls.__subclasses__():
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if name == sub_cls.__name__.lower():
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return sub_cls()
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@abc.abstractmethod
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def speak(self):
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""""""
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class Kitty(Pet):
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def speak(self):
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return "Miao"
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class Duck(Pet):
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def speak(self):
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return "Quak"
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return random.choice([Dog, Cat])()
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# Show pets with various factories
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if __name__ == "__main__":
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# A Shop that sells only cats
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cat_shop = PetShop(Cat)
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cat_shop.show_pet()
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print("")
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# A shop that sells random animals
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shop = PetShop(random_animal)
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for i in range(3):
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shop = PetShop(get_factory())
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shop.show_pet()
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print("=" * 20)
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for name0 in ["kitty", "duck"]:
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pet = Pet.from_name(name0)
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print("{}: {}".format(name0, pet.speak()))
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### OUTPUT ###
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# We have a lovely Cat
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# It says meow
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# We also have cat food
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# ====================
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#
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# We have a lovely Dog
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# It says woof
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# We also have dog food
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# ====================
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# We have a lovely Cat
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# It says meow
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# We also have cat food
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# ====================
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# kitty: Miao
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# duck: Quak
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# We have a lovely Cat
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# It says meow
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# ====================

‎tests/test_abstract_factory.py‎

Lines changed: 5 additions & 53 deletions
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,7 @@
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#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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import unittest
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from creational.abstract_factory import PetShop,\
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Dog, Cat, DogFactory, CatFactory, Pet
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from creational.abstract_factory import PetShop, Dog
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try:
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from unittest.mock import patch
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except ImportError:
@@ -12,54 +11,7 @@
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class TestPetShop(unittest.TestCase):
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1413
def test_dog_pet_shop_shall_show_dog_instance(self):
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f = DogFactory()
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with patch.object(f, 'get_pet') as mock_f_get_pet,\
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patch.object(f, 'get_food') as mock_f_get_food:
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ps = PetShop(f)
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ps.show_pet()
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self.assertEqual(mock_f_get_pet.call_count, 1)
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self.assertEqual(mock_f_get_food.call_count, 1)
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def test_cat_pet_shop_shall_show_cat_instance(self):
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f = CatFactory()
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with patch.object(f, 'get_pet') as mock_f_get_pet,\
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patch.object(f, 'get_food') as mock_f_get_food:
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ps = PetShop(f)
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ps.show_pet()
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self.assertEqual(mock_f_get_pet.call_count, 1)
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self.assertEqual(mock_f_get_food.call_count, 1)
31-
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33-
class TestCat(unittest.TestCase):
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@classmethod
36-
def setUpClass(cls):
37-
cls.c = Cat()
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39-
def test_cat_shall_meow(cls):
40-
cls.assertEqual(cls.c.speak(), 'meow')
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42-
def test_cat_shall_be_printable(cls):
43-
cls.assertEqual(str(cls.c), 'Cat')
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45-
46-
class TestDog(unittest.TestCase):
47-
48-
@classmethod
49-
def setUpClass(cls):
50-
cls.d = Dog()
51-
52-
def test_dog_shall_woof(cls):
53-
cls.assertEqual(cls.d.speak(), 'woof')
54-
55-
def test_dog_shall_be_printable(cls):
56-
cls.assertEqual(str(cls.d), 'Dog')
57-
58-
59-
class PetTest(unittest.TestCase):
60-
61-
def test_from_name(self):
62-
test_cases = [("kitty", "Miao"), ("duck", "Quak")]
63-
for name, expected_speech in test_cases:
64-
pet = Pet.from_name(name)
65-
self.assertEqual(pet.speak(), expected_speech)
14+
dog_pet_shop = PetShop(Dog)
15+
with patch.object(Dog, 'speak') as mock_Dog_speak:
16+
dog_pet_shop.show_pet()
17+
self.assertEqual(mock_Dog_speak.call_count, 1)

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