Advanced Arguments

Why advanced arguments exist

Sometimes you want a function that accepts any number of inputs. Python gives you *args for extra positional arguments and **kwargs for extra keyword arguments.

Using *args

*args collects extra positional values into a tuple.

python
def total(*args):
    return sum(args)

print(total(1, 2, 3))

Using **kwargs

**kwargs collects extra keyword values into a dictionary.

python
def build_profile(**kwargs):
    return kwargs

print(build_profile(name="Lina", age=28))

Parameter order matters

The usual order is: normal parameters, *args, keyword-only parameters, then **kwargs.

python
def greet(greeting, *names, punctuation="!"):
    for name in names:
        print(greeting, name + punctuation)

Keyword-only parameters

You can force a parameter to be keyword only with a *.

python
def save(path, *, overwrite=False):
    print(path, overwrite)

save("file.txt", overwrite=True)

Unpacking when calling

You can unpack a list or dict into function arguments.

python
nums = [1, 2, 3]
print(total(*nums))

options = {"sep": "-", "end": "!"}
print("a", "b", **options)

Common mistakes to avoid

• Forgetting that *args is a tuple, not a list.
• Passing the same argument twice (once positionally and once by name).
• Putting **kwargs before *args in the function signature.

What you should understand after this lesson

• When and why to use *args and **kwargs.
• How to enforce keyword-only parameters.
• How to unpack sequences and dictionaries when calling functions.