It looks like there is a line in the docs that prevents the docs from building under python3 https://github.com/pyatom/pyatom/blob/a170717408d46f5d872585a877ffd8ee09a1a052/doc/conf.py#L72 compare to what's going on in `setup.py` https://github.com/pyatom/pyatom/blob/a170717408d46f5d872585a877ffd8ee09a1a052/setup.py#L22 Gonna fix this in a PR in a second.