Returning function from another function

March 17, 2022

I’m developing a package in which I want to modify incoming functions to add extra functionality. I’m not sure how I would go about doing this. A simple example of what I’m trying to do:

def function(argument):
    print(argument,end=",")

# this will not work but an attempt at illustrating what I wish to accomplish
def modify_function(original_function):
    return def new_function(arguments):
               for i in range(3):
                   original_function(arguments)
               print("finished",end="")

and running the original function:

function("hello")

gives the output: hello,

and running the modified function:

modified_function = modify_function(function)
modified_function(i)

gives the output: hello,hello,hello,finished

>Solution :

Credit to @Matiss for pointing out the way to do this. Adding this answer so it is documented.

def original_function(argument):
    print(argument, end=",")

def modify_function(input_func):
    # Using *args and **kwargs allows handling of multiple arguments
    # and keyword arguments, in case something more general is required.
    def new_func(*args, **kwargs):
        for i in range(3):
            input_func(*args, **kwargs)
        print("finished", end="")

    return new_func

modified_function = modify_function(original_function)
modified_function("hello")

For other kinds of modification where you want to e.g. fix some of the arguments passed in, this way will still work, but you may also make use of https://docs.python.org/3/library/functools.html#functools.partial.