Where are the best online communities centered around data science/machine learning or python?

I think Twitter is great to stay in touch and see what other people are up to, and to share news of course. Cross-validated & Quora are good websites to ask specific questions and collect multiple opinions about a topic. There’s also a machine learning group on Google+ that has a lot of members, but is not that active anymore I fear. The MachineLearning subreddit is another nice place to discuss certain news and articles.