Decorator 정리 및 예시

• ref: https://www.datacamp.com/community/tutorials/decorators-python

1. decorator 기본구성

• A: enclosing func
• B: nested func
• C: func as arg

2. 작동

• Call C
• Pass C into A as arg
• A return B
• B do something using C

3. code example

• func basic

  def plus_one(num):
      return num + 1
  
  plus_one(5)
  >> 6

• func call another func

  def plus_one(num):
      def add_one(num):
          return num + 1
  
      result = add_one(num)
      return result
  plus_one(1)
  >> 2

• func as arg

  def plus_one(num):
      return num + 1
  
  def func_call(func):
      num_to_add = 5
      return func(num_to_add)
  
  func_call(plus_one)
  >> 6

• func nesting another func

  def hello_func():
      def say_hi():
          return "Hi"
      return say_hi()
  
  hello_func()
  >> 'Hi'

• nested function access the outer scope of the enclosing func

  # a critical concept in decorators:
  # nested function access the outer scope of the enclosing func
  def print_msg(msg):
      def msg_sender():
          print(msg)
      msg_sender()
  
  print_msg('yes')
  >> yes

step1

• decorator without args

# Nested func use outer func's variable
# which is func as agrs
# Enclosing func
def uppercase_decorator(func):
    def wrapper():
        return func().upper()
    return wrapper

@uppercase_decorator
def say():
    return 'hello there'
say()

'HELLO THERE'

step2

• decorator which accept args

def dec_with_args(func):
    def nested_accept_args(arg1, arg2):
        print('ars: {}, {}'.format(arg1, arg2))
        func(arg1, arg2)
    return nested_accept_args

@dec_with_args
def cities(first, second):
    print('cities: {}, {}'.format(first, second))

cities('sun', 'moon')

ars: sun, moon
cities: sun, moon

step3

• decorator which accept as many args as user would like

def dec_pass_arbitrary_args(func):
    def wrapper(*args, **kwargs):
        print('the positional args are', args)
        print('the keword args are', kwargs)
        func(*args)
    return wrapper

# with positional args
@dec_pass_arbitrary_args
def func_with_args(a, b, c):
    print(a, b, c)

func_with_args(1,2,3)

the positional args are (1, 2, 3)
the keword args are {}
1 2 3

@dec_pass_arbitrary_args
def func_with_kwargs():
    print('this has keyword args')

func_with_kwargs(name='Roy', age='12')

the positional args are ()
the keword args are {'name': 'Roy', 'age': '12'}
this has keyword args

step4

• dec within wrapper passing dec_args

def dec_wrapper(*dec_args):
    def dec(func):
        "decorator we code above"

        def wrapper(*func_args):
            print("dec positional args: ", dec_args)
            print("func positional args: ", func_args)
            return func(*func_args)

        return wrapper

    return dec

@dec_wrapper('dec1', 'dec2')
def func1(*args):
    print('this is from func1', args)
func1('func1', 'func2')

dec positional args:  ('dec1', 'dec2')
func positional args:  ('func1', 'func2')
this is from func1 ('func1', 'func2')

step5

• decorator which measure the execution time

import time
def timeit(func):
    def wrapper(*args, **kwargs):
        print('strat timeit')

        ts = time.time()
        result = func(*args)
        te = time.time()

        print(func.__name__, te-ts)
        return result
    return wrapper

@timeit
def multiply_nums(*num):
    print('start multiply func')
    i = 1
    for j in num:
        i *= j
    return i

res = multiply_nums(1,2,3)
print(res)

strat timeit
start multiply func
multiply_nums 4.982948303222656e-05
6