How to install packages in psychopy in Mac

I would like to install the PyQt5 package in psychopy in a Mac, but it seems that installing packages beyond the defaults in psychopy is tricky, especially in Macs. This is somewhat more tricky because I think PyQt5 is in fact a default package in psychopy, but on my old Mac operating system I get an error saying it’s not installed. I’m running Mac OS 10.6 series.

The new Python3 version of PsychoPy Standalone includes PyQt5.

In general, adding packages to PsychoPy is described here: http://www.psychopy.org/recipes/addCustomModules.html

But the specific case of PyQt5 if you’re trying to use Python 2.7 is very painful to build if I remember correctly.

How do you make sure you’re running the Python 3 version instead of 2.7?