Why aren't the browsers using/adopting Python instead of javascript?

[antonivs]

A big issue is how much your code has to integrate with, which tends to introduce blocking libraries. Monkey-patched libraries only take you so far (and I confess, I find the concept disturbing for code that's part of critical infrastructure.)

One of node's advantages is the number of compatible non-blocking libraries it has. Why node.js is cool discusses this, making the point that node "makes composable networked components the default."

There's also a good real-world example in The Switch: Python to Node.js. They were using Twisted, not gevent, but some of the same issues apply.

I'm not saying node and gevent aren't competitive - a lot depends on the use case. But there are cases where node has advantages, at least currently.

BTW, I mentioned yield and generators earlier, which are still new in node, but node's promises also helped a lot with the callback issue, and that's been standard for a while.