Function signatures should include slash and star: https://github.com/python/devguide/pull/1344
Summary
If a function accepts positional-only or keyword-only arguments, include the slash and the star in the signature as appropriate.
.. function:: some_function(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
Although the syntax is terse, it is precise about the allowable ways to call the function and is taken from Python itself.
The CPython Devguide has been updated to reflect this recommendation.