How to filter nodes with names that match a pattern or only nodes connected to such nodes with gvpr/graphviz?

I have a DOT file, say bar.dot. How do I use gvpr to output a graph as described below?

• let A be the set of nodes in bar.dot with names that contain foo
• the graph should only contain nodes in A or nodes directly connected to at least one node in A

I haven't tried anything yet because I'm not sure how to proceed with this problem. I have access to graphviz if that solves this better.

I ended up using pygraphviz instead: https://github.com/pygraphviz/pygraphviz. I'm more familiar with Python and this library is sufficiently documented.