I have attached a *possible* new version of threading.py
that returns the value of the target.

run's calling function needs to return.

Hi! I'm not sure what feature exactly you're proposing here, but please follow the devguide's guidelines to submit a proper patch:
http://docs.python.org/devguide/patch.html
And more generally:
http://docs.python.org/devguide/

What is your use case? I think this can easily be implemented by subclassing the threading.Thread class:

    class MyThread(threading.Thread):

        def run(self):
            # skip try...finally to make the example shorter
            result = None
            if self._target:
                result = self._target(*self._args, **self._kwargs)
            return result

We can reopen this if you can share a valid use case. Thanks for the report!