The problem

In Python, we can pass arguments to a function with “args” and “kwargs”.

Imagine you want to create a function that computes the product of all its arguments. The naive approach is the following:

def product(a=1, b=1, c=1, d=1, e=1, f=1):
    return a * b * c * d * e * f

If we want to pass exactly 6 arguments, this function will work properly. However, we can doubt that this will be possible if we want to pass a greater number of arguments.

A solution would be to pass the arguments in a tuple, a list, or any other data structure. We will see that this is possible natively with args and kwargs.

Args

Let’s see how we can transform our product function into a function with args.

def product(*args):
    res = 1
    for arg in args:
        res *= arg
    return res

product(1, 2, 3, 4, 5, 6)

Args being a tuple, we can now add as many arguments as we want to the function, the result will be the product of all these arguments.

args (and Kwargs) is only a variable name, it is possible to write the function def product(*dict) if you prefer. The important thing is the asterisk.

Kwargs

There is no big difference between kwargs and args. Kwargs means Keyword Arguments.

def product(**kwargs):
    res = 1
    for key, value in kwargs.items(): # kwargs is a dictionary
        res *= value
    return res

product(a=1, b=2, c=3, d=4, e=5, f=6)

Kwargs is a dictionary. We can now add as many key/value pairs as we want to the function, the result will be the product of all these values.

For this purpose, args is of course a better choice than kwargs.

Kwargs and Args in the same function.

Remark

In python, “optional arguments” (with default values) are placed at the end.

def product(a, b, c=1, d=1, e=1, f=1):
    return a * b * c * d * e * f

product(1, 2)

Il n’est pas possible de passer c=1 avant b. Cela retounerait une erreur.

Both kwargs and args

As seen, there is an order in the arguments of a function. The order is the following:

1. Standard arguments
2. Optional arguments
3. *args
4. **kwargs

Thus, for the following function :

def showNumbers(a, b, *c, **d):
    print(a)
    print(b)
    print(c)
    print(d)

showNumbers(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, postFinalNumber = 19, finalNumber = 20)

Results in:

1
2
(3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
{'postFinalNumber': 19, 'finalNumber': 20}