VIS-Ualizer is a JavaScript based visualiation extension for the VIS-Framework based on D3.js, Flask, and Flask-API. VIS-Ualizer can be used in lieu of matplotlib in conjunction with the VIS-Framework, or perhaps music21, and will eventually become part of the Rodan-Client.
VIS-Ualizer also ouputs various types of score representations, such as a piano roll, and a traditional score output (in modern notation, for right now) via Verovio.