Thanks for the invite; I have not worked on Node much; but if you are building an app that requires a lot of statistical computations in the back-end; you could go with Python, just because of the sheer number of options, if you look at all the Python libraries which aid you in doing stats easy.

Otherwise it won't matter much I would say with the current perspective that I have.

The only time I will suggest you use Node.js over python is when it involves a real-time application. This is due to the fact that node can handle real-time concurrency better than python. But apart from that, it's all personal preference.