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什么是python的装饰器?

网络上的定义:
装饰器就是一函数,用来包装函数的函数,用来修饰原函数,将其重新赋值给原来的标识符,并永久的丧失原函数的引用。

最能说明装饰器的例子如下:

复制代码 代码如下:

#-*- coding: UTF-8 -*-
import time

def foo():
    print 'in foo()'

# 定义一个计时器,传入一个,并返回另一个附加了计时功能的方法
def timeit(func):

    # 定义一个内嵌的包装函数,给传入的函数加上计时功能的包装
    def wrapper():
        start = time.clock()
        func()
        end =time.clock()
        print 'used:', end - start

    # 将包装后的函数返回
    return wrapper

foo = timeit(foo)
foo()

python中提供了一个@符号的语法糖,用来简化上面的代码,他们的作用一样

复制代码 代码如下:

import time

def timeit(func):
    def wrapper():
        start = time.clock()
        func()
        end =time.clock()
        print 'used:', end - start
    return wrapper

@timeit
def foo():
    print 'in foo()'

foo()

这2段的代码是一样的,等价的。

内置的3个装饰器,他们分别是staticmethod,classmethod,property,他们的作用是分别把类中定义的方法变成静态方法,类方法和属性,如下:

复制代码 代码如下:

class Rabbit(object):

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

    @staticmethod
    def newRabbit(name):
        return Rabbit(name)

    @classmethod
    def newRabbit2(cls):
        return Rabbit('')

    @property
    def name(self):
        return self._name

装饰器的嵌套:
就一个规律:嵌套的顺序和代码的顺序是相反的。
也是来看一个例子:

复制代码 代码如下:

#!/usr/bin/python
# -*- coding: utf-8 -*-

def makebold(fn):
    def wrapped():
        return "" + fn() + ""
    return wrapped

def makeitalic(fn):
    def wrapped():
        return "" + fn() + ""
    return wrapped

@makebold
@makeitalic
def hello():
    return "hello world"

print hello()

返回的结果是:
hello world
为什么是这个结果呢?
1.首先hello函数经过makeitalic 函数的装饰,变成了这个结果hello world
2.然后再经过makebold函数的装饰,变成了hello world,这个理解起来很简单。

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