@daxlab, thanks for your PR! By analyzing the history of the files in this pull request, we identified @birkenfeld, @benjaminp and @rhettinger to be potential reviewers.

Please update the docstring.

And what is more correct,

if *ndigits* is omitted or is ``None``

(as in the first paragraph), or

if *ndigits* is omitted or ``None``

(as in the second paragraph)? Or both are correct?

if *ndigits* is omitted or ``None`` looks correct.

About

if ndigits is omitted or is None

versus

if ndigits is omitted or None

I think either is fine. To my eyes, the first looks a bit clearer, but also a bit more pedantic.

@serhiy-storchaka docs updated.

@serhiy-storchaka plz review. Also, should I send a separate PR to 3.6 branch or you can cherry-pick ?

The current changes LGTM, but see a discussion on the tracker. Perhaps the documentation needs additional clarification.

Based on more recent discussion on the tracker, it looks these proposed changes have now been addressed by other PRs, primarily #6342 and #2740. Thanks for starting the ball rolling @daxlab!