*args and **kwargs

Any number of arguments

*args collects every extra positional argument into a tuple:

def total(*numbers):
    return sum(numbers)

total(1, 2, 3)     # 6
total()            # 0

**kwargs collects every extra keyword argument into a dictionary:

def describe(**details):
    return details

describe(name="Ada", age=36)   # {"name": "Ada", "age": 36}

The names args and kwargs are only convention — the * and ** do the work.

The same symbols work in reverse at the call site, spreading a list or dictionary out into arguments:

numbers = [1, 2, 3]
total(*numbers)       # same as total(1, 2, 3)

Your turn: write summarise(*values, **options) returning a dictionary with the count of values, their total, and a label taken from the options (defaulting to "summary").

Spreading arguments

* and ** at a call site do the opposite of what they do in a definition: they unpack a collection into separate arguments.

def make(name, colour):
    return f"{colour} {name}"

parts = {"name": "car", "colour": "red"}
make(**parts)     # "red car"

This is how wrapper functions pass whatever they were given straight through.

Your turn: write apply_all(fn, arg_lists) where arg_lists is a list of argument lists. Call fn once per entry, spreading each list, and return the results.