code: def _recurse_find_trace(self, structure, item, trace=[]):
          
  
          try:
              i = structure.index(item)
          except ValueError:
              for j,substructure in enumerate(structure):
                  if isinstance(substructure, list):
                      return self._recurse_find_trace(substructure, item, trace+[j])
          else:
              return trace+[i]
docs: given a nested structure from _parse_repr and find the trace route to get to item