27 – Enforce keyword arguments for options

You can use a single asterisk * in a function definition to force all following arguments to be keyword-only.

This is particularly helpful for arguments that act as options or as configuration values. Here is an example with a function that can return the temperature in a room in two units, Celsius and Fahrenheit:

def get_temperature(room, *, unit)

By using *, the second argument must be passed as a keyword argument:

get_temperature("bedroom", unit="celsius")  # This works.

If you don’t, you get an exception TypeError:

get_temperature("bedroom", "celsius")  # TypeError