After a call to join() method on a Threading.thread object,there is no
way to successfully call start() method on it.

Indeed, the __started flag is not reset in the theading.Thread join()
method. 
Since the start() method checks for __started flag , this flag is always  
true after a first start, despite the thread was effectively stopped by
the join() call

Since it's perfectly legal to store a threading.Thread object in a
variable or an object member, i think the join() behaviour is odd
because it prevents instance reusability.