matplotlib broken after `pip install matplotlib --upgrade` to version 2.1.0
This is an issue with matplotlib 2.1.0 on macOS. There is a bug which causes this due to some refactoring in the new release. 

It will probably be fixed in a bug fix release soon, but you will have to downgrade if you need it working now.

To install old version: pip uninstall matplotlib &amp;&amp; pip install matplotlib==2.0.2

Refs:


https://github.com/matplotlib/matplotlib/issues/9345
https://github.com/matplotlib/matplotlib/issues/9366
https://github.com/matplotlib/matplotlib/pull/9347