python进阶（18）@wraps装饰器前言案例使用wraps装饰器解决

前言

我们都知道装饰器的作用是在不改变原有的代码基础上，添加新的功能，但是这样会有一个弊端，被装饰的函数某些属性会变改变，接下来我们来看下

案例

复制代码import time def run_time(func): def wrapper(*args, **kwargs): """时间装饰器""" time1 = time.time() func(*args, **kwargs) time2 = time.time() cost_time = time2 - time1 return f"函数花了{cost_time}秒" return wrapper @run_time def test(): """测试""" print([i for i in range(1, 100001) if i % 200 == 0]) if __name__ == '__main__': print(test.__name__) print(test.__doc__) """ 结果 # wrapper # 时间装饰器 """

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import time


def run_time(func):
    def wrapper(*args, **kwargs):
        """时间装饰器"""
        time1 = time.time()
        func(*args, **kwargs)
        time2 = time.time()
        cost_time = time2 - time1
        return f"函数花了{cost_time}秒"
    return wrapper


@run_time
def test():
    """测试"""
    print([i for i in range(1, 100001) if i % 200 == 0])


if __name__ == '__main__':
    print(test.__name__)   
    print(test.__doc__)  
"""
结果
# wrapper
# 时间装饰器
"""

可以看到，我们明明打印的是test函数的__name__属性，最后显示的却是run_time的属性。
我们知道@run_time装饰器实际上就等于test = run_time(test)，此时我们打印test.__name__实际上test已经指向了wrapper，这样会造成我们打印的时候会打印装饰器的内嵌函数的名字和注释。

使用wraps装饰器解决

wraps可以将原函数对象的指定属性复制给包装函数对象, 默认有 __module__、__name__、__doc__、__qualname__、__annotations__或者通过参数选择

复制代码import time from functools import wraps def run_time(func): @wraps(func) def wrapper(*args, **kwargs): """时间装饰器""" time1 = time.time() func(*args, **kwargs) time2 = time.time() cost_time = time2 - time1 return f"函数花了{cost_time}秒" return wrapper @run_time def test(): """测试""" print([i for i in range(1, 100001) if i % 200 == 0]) if __name__ == '__main__': print(test.__name__) print(test.__doc__) """ 结果： test 测试 """

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import time
from functools import wraps


def run_time(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        """时间装饰器"""
        time1 = time.time()
        func(*args, **kwargs)
        time2 = time.time()
        cost_time = time2 - time1
        return f"函数花了{cost_time}秒"
    return wrapper


@run_time
def test():
    """测试"""
    print([i for i in range(1, 100001) if i % 200 == 0])


if __name__ == '__main__':
    print(test.__name__)   
    print(test.__doc__) 
"""
结果：
test
测试
"""

我们就只在原来的wrapper内函数上加了一个@wraps(func)装饰器，就可以打印出我们想要的结果了，这是因为wraps可以将原函数对象的指定属性复制给包装函数对象，我们可以查看它的源码

复制代码def wraps(wrapped, assigned = WRAPPER_ASSIGNMENTS, updated = WRAPPER_UPDATES): """Decorator factory to apply update_wrapper() to a wrapper function Returns a decorator that invokes update_wrapper() with the decorated function as the wrapper argument and the arguments to wraps() as the remaining arguments. Default arguments are as for update_wrapper(). This is a convenience function to simplify applying partial() to update_wrapper(). """ return partial(update_wrapper, wrapped=wrapped, assigned=assigned, updated=updated)

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def wraps(wrapped,
          assigned = WRAPPER_ASSIGNMENTS,
          updated = WRAPPER_UPDATES):
    """Decorator factory to apply update_wrapper() to a wrapper function

       Returns a decorator that invokes update_wrapper() with the decorated
       function as the wrapper argument and the arguments to wraps() as the
       remaining arguments. Default arguments are as for update_wrapper().
       This is a convenience function to simplify applying partial() to
       update_wrapper().
    """
    return partial(update_wrapper, wrapped=wrapped,
                   assigned=assigned, updated=updated)