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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def UnregisterMessageHandler(self, timeout=None):
 """Unregisters any registered message handler."""

    if self.handler_thread:
      self.handler_stop = True
      self.handler_thread.join(timeout)
      if self.handler_thread.isAlive():
        raise RuntimeError("Message handler thread did not join in time.")
      self.handler_thread = None