code: def next_event_description(self):
          
          if self._fancy_heap.size == 0:
              event_type = 'Nothing'
              edge_index = None
          else:
              s = [q._key() for q in self.edge2queue]
              s.sort()
              e = s[0][1]
              q = self.edge2queue[e]
  
              event_type = 'Arrival' if q.next_event_description() == 1 else 'Departure'
              edge_index = q.edge[2]
          return event_type, edge_index
docs: Returns whether the next event is an arrival or a departure
          and the queue the event is accuring at.
  
          Returns
          -------
          des : str
              Indicates whether the next event is an arrival, a
              departure, or nothing; returns ``'Arrival'``,
              ``'Departure'``, or ``'Nothing'``.
          edge : int or ``None``
              The edge index of the edge that this event will occur at.
              If there are no events then ``None`` is returned.