8.1. Decorator About

  • Decorator is an object, which takes another object as it's argument

  • Since Python 2.4: PEP 318 -- Decorators for Functions and Methods

  • Since Python 3.9: PEP 614 -- Relaxing Grammar Restrictions On Decorators

  • Decorator can do things before call

  • Decorator can do things after call

  • Decorator can modify arguments

  • Decorator can modify returned value

  • Decorator can avoid calling

  • Decorator can modify globals

  • Decorator can add or change metadata

../../_images/decorator-about-call1.png

8.1.1. Syntax

  • func is a reference to function which is being decorated

  • args arbitrary number of positional arguments

  • kwargs arbitrary number of keyword arguments

  • By calling func(*args, **kwargs) you actually run original (wrapped) function with it's original arguments

>>> def mydecorator(func):
...     def wrapper(*args, **kwargs):
...         return func(*args, **kwargs)
...     return wrapper
>>>
>>>
>>> @mydecorator
... def myfunction(*args, **kwargs):
...     pass
>>>
>>>
>>> myfunction()

8.1.2. Decoration

Syntax:

>>> @mydecorator
... def myfunction(*args, **kwargs):
...     ...

Is equivalent to:

>>> myfunction = mydecorator(myfunction)