Antoine: I'm still unclear on what's going on here but I noticed something by accident when trying your example script.  Specifically, when I ran your script from the directory where it exists on disk, I could successfully reproduce what you described but if I ran your script from a different working directory (e.g. 'python3.5 ../tmp/issue_28779_repro.py') then I did not see the misbehavior and it instead ran through to completion without any exceptions reported.  I saw this phenomenon (all that I described above) on both OSX and Ubuntu 16.04 systems.

Secondly, looking at the file you attached, did everything make it into the patch?  I ask because unless I'm missing something it looks like the patch adds arguments to the function signature but does not act upon them in any new way?