python关于装饰器

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本文深入探讨了Python中的函数装饰器和类装饰器的使用方法。通过具体实例，展示了如何利用装饰器来测量函数运行时间，以及如何通过装饰器为类动态添加属性和方法，提高了代码的灵活性和复用性。

1.函数装饰器

import time


def fucker0(m):
    print(m)

    def fucker(fuc):
        def fucker2(*args, **kwargs):
            st_time=time.time()
            s=fuc(*args, **kwargs)#注意参数传递
            ed_time=time.time()
            print('程序运行时间为%s' %(ed_time-st_time))
            return s
        return fucker2
    return fucker


@fucker0('bitch') #有参装饰器
def shit(a, b=None):
    if b is None:
        b = {}
    b.update({"name": 23, 'age': 46})
    a = a**2
    time.sleep(1)
    print('程序运行结果是%s,%s' % (a, b))
    return a, b


q=shit(3, b={7:8})
print(q)
#result
bitch
程序运行结果是9,{7: 8, 'name': 23, 'age': 46}
程序运行时间为1.003929615020752
(9, {7: 8, 'name': 23, 'age': 46})

装饰器只运行一次,相当于永久改变了函数名指向的代码,因此函数嵌套是必要的
2.类的装饰器
装饰器本质上在装饰对象,python中一切皆对象.
下例利用装饰器来为类添加属性

@staticmethod
def adding(self):   # 把此函数加入类
    print('我是新增加的属性', self.b)


def Dec0(**kwargs):
    print('hahaha')
    def Dec(obj):
        for i in kwargs:
            # obj.i = kwargs[i]  # 此种方法不行,会把i当成字符串(key)
            # obj.__dict__[i] = kwargs[i]  #此种方法也不支持
            setattr(obj, i, kwargs[i])
        return obj
    return Dec


@Dec0(x=3, a4=5, adding=adding)  # 当然也可添加一个函数属性!!!
class Test:
    name= 'sabi'   # 字典的键相当于一个变量
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

t = Test(1,2,3)
t2 = Test(4,5,6)

print(t.a)
print(t.__dict__)
print(Test.x)
Test.adding(t2)
t.adding(t)

#result
hahaha
1
{'a': 1, 'b': 2, 'c': 3}
3
我是新增加的属性 5
我是新增加的属性 2

2.1关于类装饰器的一些说明

The motivating use-case was to make certain constructs more easily expressed and less reliant on implementation details of the CPython interpreter. While it is possible to express class decorator-like functionality using metaclasses, the results are generally unpleasant and the implementation highly fragile [3]. In addition, metaclasses are inherited, whereas class decorators are not, making metaclasses unsuitable for some, single class-specific uses of class decorators. The fact that large-scale Python projects like Zope were going through these wild contortions to achieve something like class decorators won over the BDFL
令人鼓舞的用案例例是使某些构造更容易表达，并且更少依赖于CPython解释器的实现细节。虽然可以使用元类表达类装饰器类功能，但结果通常令人不愉快并且实现非常脆弱。此外，元类是继承的，而类装饰器则不是，使得元类不适合类装饰器的某些特定于类的特定用途。事实上像Zope这样的大型Python项目经历了这些疯狂的扭曲，以实现类似装饰器的东西赢得了BDFL