Thank your for your response. I'm running python 3.5.2. The linked issue is indeed a duplicate of this one.

To reproduce, you can run two instances of the attached script at the same time, i.e. python3 pymkdir.py & python3 pymkdir.py. It is a race condition so won't happen every time, but with the number of directories created it should happen pretty frequently (remove the directories between tests with rm -rf 1)

I'm running Ubuntu 16.04.5 LTS. I don't know if you know anything about Ubuntu's release process, but it would be nice if the linked fix could be backported to work on that platform.