python positional argument
A function definition may look like:
def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
----------- ---------- ----------
| | |
| Positional or keyword |
| - Keyword only
-- Positional only
where / and * are optional.
If used, these symbols indicate the kind of parameter by how
the arguments may be passed to the function:
positional-only, positional-or-keyword, and keyword-only.
Keyword parameters are also referred to as named parameters.