pip install pygraphviz: No package 'libcgraph' found

sudo apt-get install python-dev graphviz libgraphviz-dev pkg-config

or the following might be needed if you're using Python 3:

sudo apt-get install python3-dev graphviz libgraphviz-dev pkg-config

then

pip install pygraphviz

For MacOS, I needed to do:

$ brew install graphviz
$ sudo pip install pygraphviz

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