Python 2 has an end-of-life date of January 1st, 2020.
Although that sounds far-off, Linux distributions are aiming to make the switch gradually. Fedora, in particular, is planning to mass-deprecate packages dependent on Python 2, with an aim to fully remove the Python 2 interpreter itself far before the cut-off date.
Our build system currently explicitly requires Python 2.7. Since it will be deprecated in the near future, we should start thinking of how to move to Python 3. At the very least, there are some test runners that we could make compatible with Python 3 early.
I'm filing this bug to make the issue a bit more visible, and add the task of transitioning test runners to Python 3 early. Probably the easiest way to do this is to change the code to support both 2 and 3.