TypeError: 'NoneType' object is not callable when passing arguments to decorator function

Question

I am trying to figure out how to use python decorators and I am trying to do so by creating my own version of the timeit command used to time a function call. This code is working

def mytimeit(f):
    def wrapper(*args, **kwargs):
        start = time.time()
        result = f(*args, **kwargs)
        print(f"Function took {time.time() - start} seconds to run.")
        return result
    return wrapper


@mytimeit
def simple_loop(n=10, sleep=0.2):
    for i in range(n):
        time.sleep(sleep)

What I want to do now is to somehow pass a parameter to that decorator. I've seen it done and it looks like I have to wrap my decorator in another function, but I cannot get that to work and I am not really sure why.

This is what I have

def mytimeit_with_args(stuff_to_print):
    def decorator(f):
        def func(*args, **kwargs):
            start = time.time()
            result = f(*args, **kwargs)
            print(stuff_to_print)
            print(f"Function took {time.time() - start} seconds to run.")
            return result
        return func

@mytimeit_with_args("just some stuff")
def harder_loop(n=10, sleep=0.2):
    for i in range(n):
        time.sleep(sleep)

The error I am getting is TypeError: 'NoneType' object is not callable

What am I not doing correctly?

Answer 1

You are actually really really close. The reason you are getting that error is because you are not returning anything at the very end of the mytimeit_with_args function, hence the NoneType is not callable error. You just need to add one return statement at the end of mytimeit_with_args like so

def mytimeit_with_args(stuff_to_print):
    def decorator(f):
        def func(*args, **kwargs):
            start = time.time()
            result = f(*args, **kwargs)
            print(stuff_to_print)
            print(f"Function took {time.time() - start} seconds to run.")
            return result
        return func
    return decorator