Sometimes you don't know how many arguments a function will get. print() is a good example — it happily takes one argument or ten.

*args

Putting * before a parameter name collects all extra positional arguments into a tuple.

def total(*numbers):
    result = 0
    for n in numbers:
        result += n
    return result

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

Inside the function, numbers is an ordinary tuple — loop it, len() it, index it. With no arguments it's simply empty.

The name args is only a convention; the * is what matters. *numbers is clearer here, and you should name it for what it holds.

You can mix normal parameters with *args, as long as the starred one comes last:

def describe(label, *values):
    print(f"{label}: {values}")

describe("Scores", 90, 85, 100)

**kwargs

Two stars collects extra keyword arguments into a dictionary.

def make_user(**details):
    return details

print(make_user(name="Ada", role="admin"))

Inside, details is a normal dictionary — use .get(), .items(), everything from Module 3.

def show(**options):
    for key, value in options.items():
        print(f"{key} = {value}")

show(theme="dark", font="mono")

Combining everything

The full order is: normal parameters, then *args, then keyword parameters with defaults, then **kwargs.

def report(title, *values, sep=", ", **meta):
    print(title)
    print(sep.join([str(v) for v in values]))
    print(meta)

report("Scores", 90, 85, 100, sep=" | ", author="Ada")

You will rarely need all four at once, but this is the order Python requires.

Unpacking when calling

The stars work in the other direction too — spreading a list or dictionary into arguments:

def add(a, b, c):
    return a + b + c

numbers = [1, 2, 3]
print(add(*numbers))

values = {"a": 1, "b": 2, "c": 3}
print(add(**values))

*numbers says "use each item as a separate positional argument." **values says "use each key/value pair as a keyword argument."

Try it yourself

Write total(*numbers) that sums however many numbers it's given.

Checkpoint

• *args collects extra positional arguments into a tuple.
• **kwargs collects extra keyword arguments into a dictionary.
• Order: normal, *args, keyword-with-default, **kwargs.
• At the call site, *list and **dict unpack into arguments.