code: def start(self, initial_delay=0):
          
          if self.listener is None:
              raise exceptions.NoAsyncListenerError
          elif self._future is not None:
              return None
  
          # Always start with 0 to trigger an immediate response for the
          # first request
          self._atv.playstatus_revision = 0
  
          # This for some reason fails on travis but not in other places.
          # Why is that (same python version)?
          # pylint: disable=deprecated-method
          self._future = asyncio.ensure_future(
              self._poller(initial_delay), loop=self._loop)
          return self._future
docs: Wait for push updates from device.
  
          Will throw NoAsyncListenerError if no listner has been set.