While debugging pull request #242, I was getting crashes on MacOS 10.13 (High Sierra). Finally chased the problem down to matplotlib-3.0.1, which was having some problems with the backend. Documenting this here so that we can see if it is an issue for others or on other platforms.

Quick fix: set the MPLBACKEND environment variable to TkAgg

export MPLBACKEND="TkAgg" 

Alternative: use matplotlib-2.2.2.