Comment 3 for bug 1732505

Summary of that Cython issue:

- it's a Cython bug where it's trying to emulate Python 2 style relative imports on Python 3
- it's fixed in master, but not in any released Cython yet
- you can work around it if you use `from __future__ import absolute_import` in your Cython modules
  and avoid explicit relative imports as well.
- an alternative fix is to make sure you compile the Cython module using language_level=3