> See the beginning of my first message, the doctest prevents me to merge a PR.


You did not show travis build link which failed other than "obj dead or exiting" error.
Don't all other errors happened only on your environment?  If no, please link to travis build link.

As far as I can confirm now, only "obj dead or exiting" error is problem in Travis.


> But I tested on the master branch without my change, and I get the same issue locally, and the issues seems to be unrelated to my change.

I suspect your environment (locale and venv used to run doctest), not your changes.

> """
> On my https://github.com/python/cpython/pull/12770 the doctest job of Travis CI failed with:
> 
> https://travis-ci.org/python/cpython/jobs/518572326
> """

Only "obj dead or exiting" happened in the job.