*args and **kwargs

• *args collects extra positional arguments into a tuple.
• **kwargs collects extra keyword arguments into a dict.

Forwarding

fn(*args, **kwargs) is how every decorator and wrapper passes arguments through transparently.

The reverse — unpacking

fn(*[1, 2, 3]) unpacks a list as positional args. fn(**{"a": 1}) unpacks a dict as keyword args.

Try it

1. Write a max_of(*nums) that returns the largest.
2. Write a build_url(host, **params) that returns host?key=value&....