Python version

[csheare]

I see that this uses Python 3, but it might be nice to specify the specific version that will work - especially for when making conda environments compatible.

I also noticed this comment in the setup.py:

NOTE: This file must remain Python 2 compatible for the foreseeable future,

to ensure that we error out properly for people with outdated setuptools

and/or pip.

Not sure if this has any affect on users python version.