Python中常用的设计模式

主要参考网址：http://www.pythontip.com/pythonPatterns/

创建型模式：

1、抽象工厂模式

class PetShop:
    def __init__(self,animal_factory=None):
        self.pet_factory = animal_factory

    def show_pet(self):
        pet = self.pet_factory.get_pet()
        print("This is a lovely",pet)

class Dog:
    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"

class Cat:
    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"

class DogFactory:
    def get_pet(self):
        return Dog()

class CatFactory:
    def get_pet(self):
        return Cat()

if __name__ == "__main__":
    shop = PetShop()
    shop.pet_factory = CatFactory()
    shop.show_pet()
    

2、单例模式

方法一：使用模块，模块是天生的单例模式，把相关的函数和数据定义在一个模块中，导入模块就可以获得一个单例对象了

方法二：使用装饰器

def Singleton(cls):
    _instance = {}

    def _singleton(*args, **kargs):
        if cls not in _instance:
            _instance[cls] = cls(*args, **kargs)
        return _instance[cls]

    return _singleton


@Singleton
class A(object):
    a = 1

    def __init__(self, x=0):
        self.x = x


a1 = A(2)
a2 = A(3)

方法三：基于__new__：

import threading
class Singleton(object):
    _instance_lock = threading.Lock()

    def __init__(self):
        pass


    def __new__(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            with Singleton._instance_lock:
                if not hasattr(Singleton, "_instance"):
                    Singleton._instance = object.__new__(cls)  
        return Singleton._instance

obj1 = Singleton()
obj2 = Singleton()
print(obj1,obj2)

def task(arg):
    obj = Singleton()
    print(obj)

for i in range(10):
    t = threading.Thread(target=task,args=[i,])
    t.start()

方法四：基于metaclass

1.类由type创建，创建类时，type的__init__方法自动执行，类() 执行type的 __call__方法(类的__new__方法,类的__init__方法)
2.对象由类创建，创建对象时，类的__init__方法自动执行，对象()执行类的 __call__ 方法

import threading

class SingletonType(type):
    _instance_lock = threading.Lock()
    def __call__(cls, *args, **kwargs):
        if not hasattr(cls, "_instance"):
            with SingletonType._instance_lock:
                if not hasattr(cls, "_instance"):
                    cls._instance = super(SingletonType,cls).__call__(*args, **kwargs)
        return cls._instance

class Foo(metaclass=SingletonType):
    def __init__(self,name):
        self.name = name


obj1 = Foo('name')
obj2 = Foo('name')
print(obj1,obj2)

3、原型模式

import copy


class Prototype:
    def __init__(self):
        self._objects = {}

    def register_object(self, name, obj):
        """Register an object"""
        self._objects[name] = obj

    def unregister_object(self, name):
        """Unregister an object"""
        del self._objects[name]

    def clone(self, name, **attr):
        """Clone a registered object and update inner attributes dictionary"""
        obj = copy.deepcopy(self._objects.get(name))
        obj.__dict__.update(attr)
        return obj


def main():
    class A:
        pass

    a = A()
    prototype = Prototype()
    prototype.register_object('a', a)
    b = prototype.clone('a', a=1, b=2, c=3)

    print(a)
    print(b.a, b.b, b.c)


if __name__ == '__main__':
    main()

结构型模式：

1、适配器模式

class Dog:
    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"

class Cat:
    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"

class Adaptor:
    def __init__(self,obj,adapted_methods):
        self.obj= obj
        self.__dict__.update(adapted_methods)
    def __getattr__(self,attr):
        return getattr(self.obj,attr)

if __name__ == "__main__":
    objects = []
    dog = Dog()
    objects.append(Adaptor(dog,dict(make_noise=dog.speak)))
    
    for obj in objects:
        print(obj,obj.make_noise())

2、装饰模式

class foo(object):
    def f1(self):
        print("original f1")

    def f2(self):
        print("original f2")


class foo_decorator(object):
    def __init__(self, decoratee):
        self._decoratee = decoratee

    def f1(self):
        print("decorated f1")
        self._decoratee.f1()

    def __getattr__(self, name):
        return getattr(self._decoratee, name)

u = foo()
v = foo_decorator(u)
v.f1()
v.f2()

3、代理模式

class SalesManager:
    def work(self):                         
        print("Sales Manager working...")             

    def talk(self):                         
        print("Sales Manager ready to talk") 


class Proxy:
    def __init__(self):                         
        self.busy = 'No'                         
        self.sales = None             

    def work(self):
        print("Proxy checking for Sales Manager availability")                         
        if self.busy == 'No':                                      
            self.sales = SalesManager()                                      
            time.sleep(2)
            self.sales.talk()                         
        else:                                      
            time.sleep(2)
            print("Sales Manager is busy")


if __name__ == '__main__':
    p = Proxy()
    p.work()
    p.busy = 'Yes'
    p.work()

4、外观模式

import time

SLEEP = 0.5


# Complex Parts
class TC1:
    def run(self):
        print("###### In Test 1 ######")
        time.sleep(SLEEP)
        print("Setting up")
        time.sleep(SLEEP)
        print("Running test")
        time.sleep(SLEEP)
        print("Tearing down")
        time.sleep(SLEEP)
        print("Test Finished\n")


class TC2:
    def run(self):
        print("###### In Test 2 ######")
        time.sleep(SLEEP)
        print("Setting up")
        time.sleep(SLEEP)
        print("Running test")
        time.sleep(SLEEP)
        print("Tearing down")
        time.sleep(SLEEP)
        print("Test Finished\n")


class TC3:
    def run(self):
        print("###### In Test 3 ######")
        time.sleep(SLEEP)
        print("Setting up")
        time.sleep(SLEEP)
        print("Running test")
        time.sleep(SLEEP)
        print("Tearing down")
        time.sleep(SLEEP)
        print("Test Finished\n")


# Facade
class TestRunner:
    def __init__(self):
        self.tc1 = TC1()
        self.tc2 = TC2()
        self.tc3 = TC3()
        self.tests = [i for i in (self.tc1, self.tc2, self.tc3)]

    def runAll(self):
        [i.run() for i in self.tests]


# Client
if __name__ == '__main__':
    testrunner = TestRunner()
    testrunner.runAll()

行为型模式：

1、观察者模式

class Subject(object):
    def __init__(self):
        self._observers = []

    def attach(self, observer):
        if not observer in self._observers:
            self._observers.append(observer)

    def detach(self, observer):
        try:
            self._observers.remove(observer)
        except ValueError:
            pass

    def notify(self, modifier=None):
        for observer in self._observers:
            if modifier != observer:
                observer.update(self)


# Example usage
class Data(Subject):
    def __init__(self, name=''):
        Subject.__init__(self)
        self.name = name
        self._data = 0

    @property
    def data(self):
        return self._data
    
    @data.setter
    def data(self, value):
        self._data = value
        self.notify()


class HexViewer:
    def update(self, subject):
        print('HexViewer: Subject %s has data 0x%x' %
              (subject.name, subject.data))


class DecimalViewer:
    def update(self, subject):
        print('DecimalViewer: Subject %s has data %d' %
              (subject.name, subject.data))


# Example usage...
def main():
    data1 = Data('Data 1')
    data2 = Data('Data 2')
    view1 = DecimalViewer()
    view2 = HexViewer()
    data1.attach(view1)
    data1.attach(view2)
    data2.attach(view2)
    data2.attach(view1)

    print("Setting Data 1 = 10")
    data1.data = 10
    print("Setting Data 2 = 15")
    data2.data = 15
    print("Setting Data 1 = 3")
    data1.data = 3
    print("Setting Data 2 = 5")
    data2.data = 5
    print("Detach HexViewer from data1 and data2.")
    data1.detach(view2)
    data2.detach(view2)
    print("Setting Data 1 = 10")
    data1.data = 10
    print("Setting Data 2 = 15")
    data2.data = 15


if __name__ == '__main__':
    main()

2、访问者模式

class Node(object):
    pass


class A(Node):
    pass


class B(Node):
    pass


class C(A, B):
    pass


class Visitor(object):
    def visit(self, node, *args, **kwargs):
        meth = None
        for cls in node.__class__.__mro__:
            meth_name = 'visit_'+cls.__name__
            meth = getattr(self, meth_name, None)
            if meth:
                break

        if not meth:
            meth = self.generic_visit
        return meth(node, *args, **kwargs)

    def generic_visit(self, node, *args, **kwargs):
        print('generic_visit '+node.__class__.__name__)

    def visit_B(self, node, *args, **kwargs):
        print('visit_B '+node.__class__.__name__)


a = A()
b = B()
c = C()
visitor = Visitor()
visitor.visit(a)
visitor.visit(b)
visitor.visit(c)

3、模板模式

ingredients = "spam eggs apple"
line = '-' * 10


# Skeletons
def iter_elements(getter, action):     
    """Template skeleton that iterates items"""      
    for element in getter():         
        action(element)     
        print(line)  


def rev_elements(getter, action):
    """Template skeleton that iterates items in reverse order"""      
    for element in getter()[::-1]:         
        action(element)     
        print(line)  


# Getters
def get_list():     
    return ingredients.split()  


def get_lists():
    return [list(x) for x in ingredients.split()]  


# Actions
def print_item(item):     
    print(item)  


def reverse_item(item):
    print(item[::-1])  


# Makes templates
def make_template(skeleton, getter, action):     
    """Instantiate a template method with getter and action"""     
    def template():         
        skeleton(getter, action)     
    return template  

# Create our template functions 
templates = [make_template(s, g, a)              
             for g in (get_list, get_lists)              
             for a in (print_item, reverse_item)              
             for s in (iter_elements, rev_elements)]  

# Execute them 
for template in templates:     
    template()

4、迭代器模式

def count_to(count):
    """Counts by word numbers, up to a maximum of five"""
    numbers = ["one", "two", "three", "four", "five"]
    # enumerate() returns a tuple containing a count (from start which
    # defaults to 0) and the values obtained from iterating over sequence
    for pos, number in zip(range(count), numbers):
        yield number

# Test the generator
count_to_two = lambda: count_to(2)
count_to_five = lambda: count_to(5)

print('Counting to two...')
for number in count_to_two():
    print(number, end=' ')

print()

print('Counting to five...')
for number in count_to_five():
    print(number, end=' ')

print()