python学习小技巧：举例讲解Python中的Null模式与桥接模式编程

Posted 2021-02-21 dasdfdfecvcx

这篇文章主要介绍了Python中的Null模式与桥接模式编程,Null模式与桥接模式都属于Python的设计模式编程,需要的朋友可以参考下
Null模式
我想每个人都有一种经历，为了获取某属性，但是有时候属性是None，那么需要你做异常处理， 而假如你想节省这样的条件过滤的代码，可以使用Null模式以减少对象是否为None的判断

python的例子
我举个不是很通用的例子，只是为了让大家理解这个模式：我有很多类， 但是不是每个类都有类方法test，所以我调用类方法就要做个异常处理，类似这样

class A(object):
pass

class B(object):
b = 1
@classmethod
def test(cls):
print cls.b

def get_test(x):
try:
return x.test
except AttributeError:
return None

# 我这里只写了2个类，但是其实有很多类
for i in [A, B]:
test = get_test(i)
# 我要判断以下是否获得了这个类方法才能决定是否可以执行
if test:
test()
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但是我用Null方法就可以这样

class Null(object):

def __init__(self, *args, **kwargs):
"忽略参数"
return None

def __call__(self, *args, **kwargs):
"忽略实例调用"
return self

def __getattr__(self, mname):
"忽略属性获得"
return self

def __setattr__(self, name, value):
"忽略设置属性操作"
return self

def __delattr__(self, name):
‘‘‘忽略删除属性操作‘‘‘
return self

def __repr__(self):
return "<Null>"

def __str__(self):
return "Null"
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还是上面的功能

class Null(object):

def __init__(self, *args, **kwargs):
"忽略参数"
return None

def __call__(self, *args, **kwargs):
"忽略实例调用"
return self

def __getattr__(self, mname):
"忽略属性获得"
return self

def __setattr__(self, name, value):
"忽略设置属性操作"
return self

def __delattr__(self, name):
‘‘‘忽略删除属性操作‘‘‘
return self

def __repr__(self):
return "<Null>"

def __str__(self):
return "Null"
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桥接模式
这个模式其实就是把产品类的实现和抽象类分离，能够灵活的变化，假如你记得状态模式,它是修改内部属性， 而桥接模式是指定好内部属性，每个产品类指定这个属性被桥接模式类调用，适用于产品类可能经常调整变化，这样还能减少了产品类之间的耦合

python的例子
这里实现一个打印操作系统名字的功能

class Bridge(object):

def __init__(self):
self.__implementation = None

def someFunctionality(self):
raise NotImplemented()

class UseCase1(Bridge):
# 根据初始化参数传入实现的产品类
def __init__(self, implementation):
self.__implementation = implementation
# 根据传入的产品类的属性打印结果
def someFunctionality(self):
print "UseCase1: ",
self.__implementation.anotherFunctionality()


class UseCase2(Bridge):
def __init__(self, implementation):
self.__implementation = implementation

def someFunctionality(self):
print "UseCase2: ",
self.__implementation.anotherFunctionality()


class ImplementationInterface:

def anotherFunctionality(self):
raise NotImplemented

# 这里其实才是实现的产品类
class Linux(ImplementationInterface):

# 它定义了这个方法，回应操作系统的名字
def anotherFunctionality(self):
print "Linux!"


class Windows(ImplementationInterface):
def anotherFunctionality(self):
print "Windows."


def main():
linux = Linux()
windows = Windows()

useCase = UseCase1(linux)
useCase.someFunctionality()

useCase = UseCase1(windows)
useCase.someFunctionality()

useCase = UseCase2(linux)
useCase.someFunctionality()

useCase = UseCase2(windows)
useCase.someFunctionality()


if __name__ == "__main__":
main()
class Bridge(object):

def __init__(self):
self.__implementation = None

def someFunctionality(self):
raise NotImplemented()

class UseCase1(Bridge):
# 根据初始化参数传入实现的产品类
def __init__(self, implementation):
self.__implementation = implementation
# 根据传入的产品类的属性打印结果
def someFunctionality(self):
print "UseCase1: ",
self.__implementation.anotherFunctionality()

class UseCase2(Bridge):
def __init__(self, implementation):
self.__implementation = implementation

def someFunctionality(self):
print "UseCase2: ",
self.__implementation.anotherFunctionality()

class ImplementationInterface:

def anotherFunctionality(self):
raise NotImplemented

# 这里其实才是实现的产品类
class Linux(ImplementationInterface):

# 它定义了这个方法，回应操作系统的名字
def anotherFunctionality(self):
print "Linux!"

class Windows(ImplementationInterface):
def anotherFunctionality(self):
print "Windows."

def main():
linux = Linux()
windows = Windows()

useCase = UseCase1(linux)
useCase.someFunctionality()

useCase = UseCase1(windows)
useCase.someFunctionality()

useCase = UseCase2(linux)
useCase.someFunctionality()

useCase = UseCase2(windows)
useCase.someFunctionality()

if __name__ == "__main__":
main()
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非常感谢你的阅读
大学的时候选择了自学python，工作了发现吃了计算机基础不好的亏，学历不行这是没办法的事，只能后天弥补，于是在编码之外开启了自己的逆袭之路，不断的学习python核心知识，深入的研习计算机基础知识，整理好了，我放在我们的微信公众号《程序员学府》，如果你也不甘平庸，那就与我一起在编码之外，不断成长吧！
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原文链接：https://blog.csdn.net/daidaiweng/article/details/105826973

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