Python Decorator

When refactoring a codes, we need to extract duplicated features from different methods or functions. A magic in Python 3 is to decorate the a striped basic functions with sharing features.

What is decorator?

A (almost) minimal demo:

from functools import wraps
def my_decorator(func):
  # to make sure func name are included.
  @wraps(func)
  def wrapper(x):
    """ function wrapper of my_decorator """
    print(" Hi, ") + func.__name__ + " return.")
    return func(x)
  return wrapper

# use decorator
@my_decorator
def foo(x):
  return x + 1

foo(10)

Why decorator?

1. Memoization: speed up function evaluation by storing the {input: output} dict.
2. Decorate a function with additional processes which probably are duplicated from other funcs. For example, you can count the evaluation times in a decorator.

Use class as a decorator

You can transform class into function by adding a __call__ method to the class.

Decorator demo:

class my_decorator:
  def __init__(self, f):
    self.f = f
  
  def __call__(self):
    print("Decorating ", self.f.__name__)
    self.f()

@my_decorator
def foo():
  print("hello from foo")

Further reading: Python3 decorators tutorial