I'm really sorry. It looks like graphviz needs to be installed from apt. I just totally thought the pypi package included the executable, but it looks like it doesn't (someone with a similar problem was here)

I believe `%sh apt install -y graphviz` should make pymc work (only on the driver node, so just for testing). When it comes to installing it to the cluster itself, I usually go to someone in the technology department to have them change whatever installation script for the cluster/startup. I believe it just does the above command but in an init script.

It's really throwing me for a loop that pypi didn't include an executable.

Let me know if this doesn't work. We'll get to the bottom of this.