Right. I found the following packages, installed in the correct order, will produce the graphs I was looking for.
1) Install Graphviz. This is a standalone package, and can be installed with e.g. brew install graphviz.
2) Install PyGraphviz using pip install pygraphviz (requires Graphviz executables)
3) Install PyDot using pip install pydot
If you want to do inline stuff in iPython Notebook, as I do, then check out this