How come sometimes Django's development server hangs?

And just keeps "waiting for s开发者_如何学JAVAerver..."

Because it's single-threaded, and you're making a second request to it from server code. Use a multithreaded or multiprocessed web server for testing instead.

EDIT:

This issue was fixed about 5 months after this question was asked; this answer no longer applies to newer versions.

Your problem might be a different reason, but at least in my case, it was due to Avast antivirus, see https://stackoverflow.com/a/47362725/122441

As a precaution, turn off your antivirus temporarily, restart runserver and see if the problem persists. At least you've eliminated one potential issue.