I want a fast way to grab a URL and parse it while streaming. Ideally this should be super fast. My language of choice is Python. I have an intuition that twisted can do this but I'm at a loss to find an example.
You only need to parse a single URL? Then don't worry. Use urllib2 to open the connection and pass the file handle into ElementTree.
Variations you can try would be to use ElementTree's incremental parser or to use iterparse, but that depends on what your real requirements are. There's "super fast" but there's also "fast enough."
It's only when you start having multiple simultaneous connections where you should look at Twisted or multithreading.
How do I fetch an XML document and parse it with Python twisted?