import threading

mydata = threading.local()

def run():
    # When will the garbage collector be able to destroy the object created
    # here? After the thread exits from ``run()``? After ``join()`` is called?
    # Or will it survive the thread in which it was created, and live until
    # ``mydata`` is garbage-collected?
    mydata.foo = object()

t = threading.Thread(target=run)
t.start()
t.join()