深入了解装饰器Decorators in python

• Decorator

  A decorator is a function that takees another function and extends the behavior of the latter function without explicitly modifying it.

• Functions

  A function returns a value based on the given arguments.

• First-Class Objects

  In Python, functions are first-class objects.

  This means that functions can be passed around and used as arguments, just like any other object (sting, int, float, list, and so on).

• Inner Functions

  Inner functions are functions defined inside other functions.

• Returning Functions From Functions

  Python also allows to use functions as return values.

  The return function without the parentheses, which means you are returning a reference to the function which returned.

• Simple Decorators

  def my_decorator(func):
      def wrapper():
          print("Something is happening before the function is called.")
          func()
          print("Something is happening after the function is called.")
      return wrapper
  
  def say_whee():
      print("Whee!")
  
  say_whee = my_decorator(say_whee)
  

  Decorators wrap a function, modifying its behavior.

• Syntactic Sugar

  The above format is a little clunky.

  Python allows you to use decorators in a simpler way with the @ symbol, sometimes called the “pie” syntax.

  The following example does the exact same thing as the first decorator example:

  def my_decorator(func):
      def wrapper():
          print("Something is happening before the function is called.")
          func()
          print("Something is happening after the function is called.")
      return wrapper
  
  @my_decorator
  def say_whee():
      print('Whee!')
  

• Reusing Decorators

  A decorator is just a regular Python function.

  It can be imported into other files.

  def do_twice(func):
      def wrapper_do_twice(*args, **kwargs):  # 输入参数
          func(*args, **kwargs)
          return func(*args, **kwargs)   # return values
      return wrapper_do_twice 
  

  For information keeping by introspection:

  import functools
  
  def do_twice(func):
      @functools.wraps(func)   # 
      def wrapper_do_twice(*args, **kwargs):
          func(*args, **kwargs)
          return func(*args, **kwargs)
      return wrapper_do_twice
  

• Fancy Decorators

• Decorating Classes

  Decorators that are built-ins in Python are @classmethod, @staticmethod, and @property.

  The @classmethod and @staticmethod decorators are used to define methods insdie a class.

  The @property decorator is used to customize getters and setters for class attributes.

• From 廖雪峰

  decorator本质上就是一个返回函数的高阶函数。

• References

1. Primer on Python Decorators
2. PEP 318 – Decorators for Functions and Methods
3. Python wiki : Decorators
4. 廖雪峰的官方网站