Python 装饰器是怎么写的-Toy模板网

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其实我们已经创建了一个装饰器！一切皆对象，那是我的对象
现在我们修改下上一个装饰器，并编写一个稍微更有用点的程序：

def a_new_decorator(a_func):
  def wrapTheFunction():
      print("I am doing some boring work before executing a_func()"
      a_func()
      print("I am doing some boring work after executing a_func()"
  return wrapTheFunction

def a_function_requiring_decoration():
    print("I am the function which needs some decoration to remove my foul smell"

a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"

a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()

a_function_requiring_decoration()
#outputs:I am doing some boring work before executing a_func()

# I am the function which needs some decoration to remove my foul smell
# I am doing some boring work after executing a_func()

这正是 Python 中装饰器做的事情！
它们封装一个函数，并且这样或者那样的方式来修改它的行。现在你也许疑惑，我们在代码里并没有使用@符号？那只是一个简短的方式来生成一个被装饰的函数。
这里是我们如何使用@来运行之前的代码：

@a_new_decorator
def a_function_requiring_decoration():
    """Hey you! Decorate me!"""
    print("I am the function which needs some decoration to "
          "remove my foul smell")
 
 a_function_requiring_decoration()
#outputs: I am doing some boring work before executing a_func()
# I am the function which needs some decoration to remove my foul smell
# I am doing some boring work after executing a_func()

#the @a_new_decorator is just a short way of saying:
a_function_requiring_decoration = a_new_decorator(a_function_requiri

希望你现在对 Python 装饰器的工作原理有个基本的理解。

如果我们运行如下代码会存在一个问题：

print(a_function_requiring_decoration.__name__)

# Output: wrapTheFunction

这并不是我们想要的！
Ouput输出应该是“a_function_requiring_decoration”。这里的函数被 warpTheFunction替代了。它重写了我们函数的名字和注释文档(docstring)。幸运的是 Python提供给我们一个简单的函数来解决这个问题，那就是functools.wraps。
我们修改上一个例子来使用functools.wraps：

from functools import wraps

def a_new_decorator(a_func):
    @wraps(a_func)
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()"
        a_func()
        print("I am doing some boring work after executing a_func()"
    return wrapTheFunction

@a_new_decorator
def a_function_requiring_decoration():
    """Hey yo! Decorate me!"""
    print("I am the function which needs some decoration to "
          "remove my foul smell")
print(a_function_requiring_decoration.__name__)
# Output: a_function_requiring_decoration

现在好多了。

我们接下来学习装饰器的一些常用场景。

from functools import wraps

def decorator_name(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        if not can_run:
            return "Function will not run"
        return f(*args, **kwargs)
     return decorated
     
@decorator_name
def func():
    return("Function is running")

can_run = True
print(func())
# Output: Function is running
can_run = False
print(func())
# Output: Function will not run