Keyword-only

Learn keyword-only parameters with *.

Keyword-only parameters

Parameters after a * become keyword-only; they cannot be passed positionally:

def create_user(name, *, role, active):
    ...

create_user("Ayse", role="admin", active=True)  # valid
create_user("Ayse", "admin", True)               # error

This makes calls readable. role and active must be given by name.

The star separates the positional region from the keyword region.

Why keyword-only?

Keyword-only parameters make calls explicit:

send_email(to, *, subject, body, cc=None)

Here subject and body cannot be passed positionally; this avoids misleading calls. send_email("a@b.com", "Merhaba", "Selam") raises an error, preventing wrong usage.

In API design this feature is common; it prevents ambiguous calls.

Exercise Write a keyword-only function

Define a function called create_user with name positional, then *, then role and active keyword-only parameters. The body does print(name, role, active). Call it with create_user("Ayse", role="admin", active=True).

Show example solution

def create_user(name, *, role, active):
    print(name, role, active)
create_user("Ayse", role="admin", active=True)

Test yourself

In def f(a, *, b): ... which call is valid?
- f(1, b=2)
- f(1, 2)
- f(a=1, 2)
- f(b=1, a=2)
Show answer

f(1, b=2) — a positional, b after the star must be keyword.

Complete the keyword-only call

create_user("Ayse", ____="admin", active=True)

Show answer

create_user("Ayse", role="admin", active=True)

Match keyword-only features

*

Region separator
keyword-only

Cannot be positional
role="admin"

Keyword call
API design

Use case

Next lesson: Positional-only

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