Python装饰器详解

王大力测试进阶之路

发布于 2019-10-25 18:08:49

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发布于 2019-10-25 18:08:49

文章被收录于专栏：橙子探索测试橙子探索测试

装饰器本质就是函数，作用是装饰其它函数，给其它函数增加附加功能，提高代码复用，减少代码量。

我们平时给函数增加新的功能时，通过修改此函数或在函数里调用新的函数实现，但是1、如果这个函数已经是上线的功能，这时修改程序原代码有很大风险 2、如果有100个这样的函数，我们就要找到100个地方进行修改。

例如：我们想新增功能，验证函数执行了多长时间，代码如下：

#修改原函数

import time
def sum1():
    start = time.clock()
    sum = 1+2
    print(sum)
    end = time.clock()
    print("time used:",end - start)
sum1()

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
3
time used: 2.9439962316848234e-05

Process finished with exit code 0


#原函数内调用新功能的函数
import time
def sum1():
    sum = 1+ 2
    print (sum)
def timeit(func):
    start = time.clock()
    func()
    end =time.clock()
    print("time used:", end - start)
timeit(sum1)

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
3
time used: 3.071996067845033e-05

Process finished with exit code 0

装饰器原则：

1、不能修改被装饰函数的源代码

2、不能修改被装饰函数的调用方式

实现装饰器储备知识：

高阶函数+嵌套函数=装饰器

1、函数即变量

def test1():
    print('hello！')
    return test1
test2=test1
test2()
print(test2)

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
hello！
<function test1 at 0x0000018E5D1A8F28>

Process finished with exit code 0

2、高阶函数

a：把一个函数名当做实参传给另外一个函数(在不修改被装饰函数源代码的情况下为其添加功能)

b：返回值中包含函数名

满足a或b就是高阶函数

def bar():
    print('in the bar')
def test1(func):
    print(func)
    func()
    return test1
test1(bar) #bar的内存地址+调用bar函数
print(test1)#test1的内存地址
print(test1(bar))#bar的内存地址+调用bar函数+test1的内存地址

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
<function bar at 0x0000026AC7C58F28>
in the bar

<function test1 at 0x0000026AC82C89D8>


<function bar at 0x0000026AC7C58F28>
in the bar
<function test1 at 0x0000026AC82C89D8>

Process finished with exit code 0




import time
def bar():
    time.sleep(3)
    print('in the bar')
def test1(func):
    start_time=time.time()
    func()
    stop_time=time.time()
    print('the func run time is %s'%(stop_time-start_time))
    return func
bar=test1(bar)
bar()


"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
in the bar
the func run time is 3.0008511543273926
in the bar

Process finished with exit code 0

3、嵌套函数

def foo():
    print('in the foo')
    def bar():
        print('in the bar')
    bar()
foo()

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
in the foo
in the bar

Process finished with exit code 0

不带参数的装饰器：

import time
def timer(func):
    def deco():
        start_time=time.time()
        func()
        stop_time=time.time()
        print('the func run time is %s'%(stop_time-start_time))
    return deco
@timer    #test1=timer(test1)
def test1():
    time.sleep(3)
    print('in the test1')
test1()


"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
in the test1
the func run time is 3.000833511352539

Process finished with exit code 0

带参数的装饰器： 从实:1中看出@timer相当于test2=timer(test2),timer(func)中func传的是test2,故func=test2 timer(test2)=deco,因为test2=timer(test2)，故test2=deco=func test2(name,age)=deco(name,age)=func(name,age)所以传参到deco和func里

实例1：
import time
def timer(func):
    def deco(*args,**kwargs):
        start_time=time.time()
        func(*args,**kwargs)
        stop_time=time.time()
        print('the func run time is %s'%(stop_time-start_time))
    return deco
@timer #test1=timer(test1)
def test1():
    time.sleep(3)
    print('in the test1')
test1()
@timer  #test2=timer(test2)
def test2(name,age):
    time.sleep(3)
    print('%s %s in the test2'%(name,age))
test2('wangli',22)

"C:\Program Files\Python35\python.exe" C:/Users/wangli/PycharmProjects/Test/Test/test.py
in the test1
the func run time is 3.0001492500305176
wangli 22 in the test2
the func run time is 3.000540256500244

Process finished with exit code 0



实例2：

import time

def timmer(flag):
    """
    :param flag: 接收装饰器的参数
    :return:
    """
    def outer_wrapper(func):
        """
        :param func: 接收被装饰的函数
        :return:
        """
        # 接收被装饰函数的参数
        def wrapper(*args, **kwargs):
            """

            :param args: 收集被装饰函数的参数
            :param kwargs: 收集被装饰函数的关键字参数
            :return:
            """
            if flag == "true":
                start_time = time.time()
                # 调用被装饰的函数
                result = func(*args, **kwargs)
                # 让进程睡一秒
                time.sleep(1)
                stop_time = time.time()
                print("{func} spend {time} ".format(func="add", time=stop_time - start_time))
                return result
            else:
                print("Unexpected ending")
        return wrapper
    return outer_wrapper

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原始发表：2019-08-06，如有侵权请联系 cloudcommunity@tencent.com 删除

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