装饰器/描述器/常用内置装饰器

装饰器：

给一个现有函数增加功能，保证参数的正确传递。

以面向对象的方式封装：

def add(x,y):
    print('Cala: %s +%s='%(x,y),end='')
    return x + y

class MyCounter:
    def __init__(self,f):
        self.func=f
        self.count=0
    def __call__(self, *args, **kwargs):
        self.count+=1
        return self.func(*args,**kwargs)

myadd=MyCounter(add)
#myadd(1,2)
print(myadd(1,2))

以函数的方式封装：

def add(x,y):
    print('Cala: %s +%s='%(x,y),end='')
    return x + y

def my_counter(f):
    def wapper(*args,**kwargs):
        wapper.counter+=1
        return f(*args,**kwargs)
    wapper.counter=0
    return wapper


myadd=my_counter(add)
print(myadd(1,2))

装饰器语法：

def my_counter(f):
    def wapper(*args,**kwargs):
        wapper.counter+=1
        return f(*args,**kwargs)
    wapper.counter=0
    return wapper


@my_counter
def minus(x,y):
    print('Cals: %s-%s=' %(x,y),end='')
    return x-y

print(minus(2,1),'	 counter:',minus.counter)
print(minus(2,1),'	 counter:',minus.counter)
print(minus(2,1),'	 counter:',minus.counter)

@my_counter
def add(x,y):
    print('Cala: %s +%s='%(x,y),end='')
    return x + y
print(add(1,2),'	 counter:',add.counter)
print(add(1,2),'	 counter:',add.counter)
print(add(1,2),'	 counter:',add.counter)

描述器

将类属性作为对象，管理一个类属性的“访问”，“修改”，“删除”

class MyAttribute:
    def __get__(self, instance, owner):
        print('get:',self,instance,owner)  #instance是实例，owner是类
    def __set__(self, instance, value):
        print('set:',self,instance,value)  #value 是赋的值
    def __delete__(self, instance):
        print('delete:',self,instance)

class Myclass:
    attr=MyAttribute()

mc=Myclass()
print('xx')
mc.attr
mc.attr=1
del mc.attr


运行结构：
xx
get: <__main__.MyAttribute object at 0x10402ed30> <__main__.Myclass object at 0x10402eeb8> <class '__main__.Myclass'>
set: <__main__.MyAttribute object at 0x10402ed30> <__main__.Myclass object at 0x10402eeb8> 1
delete: <__main__.MyAttribute object at 0x10402ed30> <__main__.Myclass object at 0x10402eeb8>

一个基于描述器的装饰器：

class Property(object):
    def __init__(self,fget=None):
        self.fget=fget
    def __get__(self, obj,objtype=None):
        if obj is None:
            return  self
        if self.fget is None:
            raise  AttributeError("unreadable attribute")
        return  self.fget(obj)

class Person():
    def __init__(self,name):
        self._name=name
        self.is_anonymous=False

    @Property
    def name(self):
        if not self.is_anonymous:
            return self._name
        else:
            return 'anonymous'

p=Person('Tuple')
print(p.name)
p.is_anonymous=True
print(p.name)

常用的内置装饰器（property):就是把一个方法变成属性的样子

class Person:
    def __init__(self,name):
        self._name=name

    @property
    def name(self):
        print("通过property来获取name")
        if hasattr(self,'_name'):
            return self._name
        else:
            raise AttributeError('没有name这个属性')

    @name.setter
    def name(self,value):
        print('通过property来设置name')
        self._name=value

    @name.deleter
    def name(self):
        print('通过propety来删除name')
        del self._name