decorator.py

decorator.py

#!/usr/bin/env python3
#
# https://realpython.com/primer-on-python-decorators/

import functools
import math

# a decorator:
# - takes a function f1 as argument
# - returns a new function f2
# - when f2 is called it will run extra code in addition to calling f1
def func_decorator(f):
    @functools.wraps(f) # preserves metadata __name__ from original function f into the returned function
    def wrapper(x):
        # modify both:
        # the function argument: x-1
        # the function result: 2*f
        return 2*f(x-1)
    return wrapper

# will be decorated manually
def func_original(x):
    return x+1

# decorated automatically:
# @func_decorator is just an easier way of saying func_original_decorated = func_decorator(func_original_decorated)
@func_decorator
def func_original_decorated(x):
    return x+1

def main():
    global func_original

    # calling decorated func manually
    print('func_original(10):', func_original(10))
    func_decorada = func_decorator(func_original)
    print('func_decorada(10):', func_decorada(10))

    # decorating manually
    print('decorating func_original manually:')
    func_original = func_decorada
    print('func_original.__name__:',func_original.__name__)
    print('func_original(10):', func_original(10))

    # func_original_decorated was decorated automatically with @func_decorator
    print('func_original_decorated.__name__:',func_original_decorated.__name__)
    print('func_original_decorated(10):', func_original_decorated(10))

    # apply a decorator to a standard library function
    print('------')
    math.factorial = debug(math.factorial)
    print('math.factorial(5):',math.factorial(5))

def debug(func):
    """Print the function signature and return value"""
    @functools.wraps(func)
    def wrapper_debug(*args, **kwargs):
        args_repr = [repr(a) for a in args]                      # 1
        kwargs_repr = [f"{k}={v!r}" for k, v in kwargs.items()]  # 2
        signature = ", ".join(args_repr + kwargs_repr)           # 3
        print(f"Calling {func.__name__}({signature})")
        value = func(*args, **kwargs)
        print(f"{func.__name__!r} returned {value!r}")           # 4
        return value
    return wrapper_debug

if __name__ == '__main__':
    main()