code: def _nodes_slots_to_slots_nodes(self, mapping):
          
          out = {}
          for node in mapping:
              for slot in node['slots']:
                  out[str(slot)] = node['id']
          return out
docs: Converts a mapping of
          {id: <node>, slots: (slot1, slot2)}
          to
          {slot1: <node>, slot2: <node>}
  
          Operation is expensive so use with caution