variadic-functions.md

Python by Example: Variadic Functions

Sometimes you want a function that accepts any number of arguments. Use *args for extra positional arguments (collected into a tuple) and **kwargs for extra keyword arguments (collected into a dict). The asterisks are the key: one for positional, two for keyword.

What you'll learn:

• *args for variable positional arguments
• **kwargs for variable keyword arguments
• When to use each

def sum_all(*args):
    return sum(args)


print(sum_all(1, 2, 3))
print(sum_all(1, 2, 3, 4, 5))


def greet(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")


greet(name="Alice", age=30)


def flexible(*args, **kwargs):
    print("args:", args)
    print("kwargs:", kwargs)


flexible(1, 2, x=10, y=20)

*args collects 1, 2, 3 into (1, 2, 3). **kwargs collects name="Alice", age=30 into {"name": "Alice", "age": 30}. The names args and kwargs are conventional; you can use others.

To run this program:

$ python source/variadic-functions.py
6
15
name: Alice
age: 30
args: (1, 2)
kwargs: {'x': 10, 'y': 20}

Tip: Put *args before **kwargs in the parameter list. Required parameters come first, then *args, then **kwargs.

Try it: Write a function that takes any number of numbers and returns their product.

Source: variadic-functions.py

Next: Lambdas