python - 了解这两个装饰器之间的区别

Question

Python 的新手并试图理解这两个装饰器之间的区别，其中装饰器 A 将其装饰的函数作为其参数，而装饰器 B 似乎将装饰后的函数传递给其自身内部的函数。

装饰器 A:

def my_decorator(some_function):

  def wrapper():

      print "Something is happening before some_function() is called."

      some_function()

      print "Something is happening after some_function() is called."

  return wrapper

@ my_decorator
def just_some_function():
  print "Wheee!"

将产生:

Something is happening before some_function() is called.
Wheee!
Something is happening after some_function() is called.
None

装饰器 B:

def decorator_factory(enter_message, exit_message):

    def simple_decorator(f):
        def wrapper():
            print enter_message
            f()
            print exit_message
        return wrapper
    return simple_decorator

@decorator_factory("Start", "End")
def hello():
    print "Hello World"

将产生:

Start
Hello World
End
None

我理解如何使用装饰器 A，some_function() 可以传递给 def wrapper() 因为 my_decorator() 需要some_function 作为参数。

但是对于装饰器 B，simple_decorator(f) 是如何接收 def hello() 返回的值的(作为 f)当 decorator_factory() 将 "start" 和 "End" 作为参数而不是 def hello() ？ Python 如何“知道”看似自动将 def hello() 传递给 simple_decorator()？

Answer 1

装饰器相当于包装它所装饰的函数。

你的例子

@decorator_factory("Start", "End")
def hello():
    print "Hello World"

hello()

与

相同

def hello():
    print "Hello World"

hello = decorator_factory("Start", "End")(hello)

hello()