4.装饰器基础篇

1.三个功能函数  f1,f2,f3

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/1/5
import time

def f1():
    for i in range(100):
        print(i)

def f2():
    for i in range(1000):
        print(i)

def f3():
    for i in range(10000):
        print(i)

2.项目遇到性能瓶颈，需要统计各个函数执行的时间

第一种解决方案（红色部分为新加代码）：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/1/5
import time

def f1():
    start_time = time.time()
    for i in range(100):
        print(i)
    end_time = time.time()
    print(end_time - start_time)

def f2():
    start_time = time.time()
    for i in range(1000):
        print(i)
    end_time = time.time()
    print(end_time - start_time)

def f3():
    start_time = time.time()
    for i in range(10000):
        print(i)
    end_time = time.time()
    print(end_time - start_time)

分析：为了统计各个函数执行的时间，修改了函数原有的代码，违反了代码设计的开放-封闭原则（对扩展开放，对修改关闭）

3.使用装饰器进行改进（红色部分为新加代码）：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/1/5
import time

def cal_consume_time(func):
    def wrapper():
        start_time = time.time()
        func()
        end_time = time.time()
        print(end_time - start_time)
    return wrapper

@cal_consume_time #等价于 f1 = cal_consume_time(f1)
def f1():
    for i in range(100):
        print(i)

@cal_consume_time #等价于 f2 = cal_consume_time(f2)
def f2():
    for i in range(1000):
        print(i)

@cal_consume_time #等价于 f3 = cal_consume_time(f3)
def f3():
    for i in range(10000):
        print(i)

分析：使用装饰器之后符合开放-关闭原则

（1）装饰器是以闭包为基础的（闭包在上一篇有介绍）；

（2）f1函数的 @cal_consume_time 这个语法糖等价于:f1 = cal_consume_time(f1)，所在以后调用 f1函数实际上调用的是 cal_consume_time(f1) 返回的函数

（3）装饰带参数的函数

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/1/5
import time

def cal_consume_time(func):
    def wrapper(*args):
        start_time = time.time()
        func(args)
        end_time = time.time()
        print(end_time - start_time)
    return wrapper

@cal_consume_time
def f1(*args):
    for i in range(100):
        print(i)
    print(args)

 （4）装饰器升级版：

# -*- coding: utf-8 -*-
#__author:jiangjing
#date:2018/1/5
import time

def cal_consume_time(flag):
    def  decprator(func):
        def wrapper(*args):
            start_time = time.time()
            func(args)
            end_time = time.time()
            if flag == True:
                print(end_time - start_time)
        return wrapper
    return decprator

@cal_consume_time(True)
def f1(*args):
    for i in range(100):
        print(i)
    print(args)

f1(-1, -2, -3)