While I’m almost done with my own modular rigging tool in python, finally I found a good reference of how a custom node editor can be written. https://github.com/golubevcg/maya_node_editor.

At the very beginning I was trying to build the entire tool into a node graph interface. This is not trivial as the coding of the UI can be a big project itself. It is really tempting to build this way for better usability. I’ve forked the project in github and hope that it would be useful in the future.