docs: def append(self, electrode_id):
          '''
          Append the specified electrode to the route.
  
          The route is not modified (i.e., electrode is not appended) if
          electrode is not connected to the last electrode in the existing route.
  
          Parameters
          ----------
          electrode_id : str
              Electrode identifier.
          '''
          do_append = False
  
          if not self.electrode_ids:
              do_append = True
          elif self.device.shape_indexes.shape[0] > 0:
              source = self.electrode_ids[-1]
              target = electrode_id
              if not (source == target):
                  source_id, target_id = self.device.shape_indexes[[source,
                                                                    target]]
                  try:
                      if self.device.adjacency_matrix[source_id, target_id]:
                          # Electrodes are connected, so append target to current
                          # route.
                          do_append = True
                  except IndexError:
                      logger.warning('Electrodes `%s` and `%s` are not '
                                     'connected.', source, target)
  
          if do_append:
              self.electrode_ids.append(electrode_id)
          return do_append