Keyword Defaults.

Second class. You can pass an argument by name: label(name="weight", unit="kg"). That is a keyword argument — order is no longer the only way.

A parameter can have a default value:

def label(name, unit="kg"):
    return f"{name} {unit}"

Then label("weight") uses "kg", and label("height", unit="m") overrides it.

Rule: parameters with defaults come after those without. Common mistake: mixing positional and keyword carelessly, or expecting a mutable default to “remember” between calls (today we only use simple string/number defaults).