Add a callback to be invoked on a session periodically.

        Args:
            callback (callable) :
                A callback function to execute periodically

            period_milliseconds (int) :
                Number of milliseconds between each callback execution.

        Returns:
            PeriodicCallback : can be used with ``remove_periodic_callback``

        .. note::
            Periodic callbacks only work within the context of a Bokeh server
            session. This function will no effect when Bokeh outputs to
            standalone HTML or Jupyter notebook cells.

def add_periodic_callback(self, callback, period_milliseconds):
        ''' Add a callback to be invoked on a session periodically.

        Args:
            callback (callable) :
                A callback function to execute periodically

            period_milliseconds (int) :
                Number of milliseconds between each callback execution.

        Returns:
            PeriodicCallback : can be used with ``remove_periodic_callback``

        .. note::
            Periodic callbacks only work within the context of a Bokeh server
            session. This function will no effect when Bokeh outputs to
            standalone HTML or Jupyter notebook cells.

        '''
        from ..server.callbacks import PeriodicCallback
        cb = PeriodicCallback(self,
                              None,
                              period_milliseconds)
        return self._add_session_callback(cb, callback, one_shot=False, originator=self.add_periodic_callback)