At this point, as a Python dev, I wouldn't even bother. The web is dirty and unless you have huge community mindshare or oodles of funding (a-la Google), you're not going to get any meaningful traction with whatever python-based UI framework you create. The JS community (funded by big players like Google and Facebook and 20 million liters of starbucks hipster coffee) has figured out all the tooling, libraries, and practically taken over every facet of the web development ecosystem so it caters for JS, that it's going to be severely impractical and hopeless to jump in at this point.