code: def get_mapping(self, superset, subset):
          
          if self._supercell:
              raise ValueError("cannot compute mapping to supercell")
          if self._primitive_cell:
              raise ValueError("cannot compute mapping with primitive cell "
                               "option")
          if len(subset) > len(superset):
              raise ValueError("subset is larger than superset")
  
          superset, subset, _, _ = self._preprocess(superset, subset, True)
          match = self._strict_match(superset, subset, 1, break_on_match=False)
  
          if match is None or match[0] > self.stol:
              return None
  
          return match[4]
docs: Calculate the mapping from superset to subset.
  
          Args:
              superset (Structure): Structure containing at least the sites in
                  subset (within the structure matching tolerance)
              subset (Structure): Structure containing some of the sites in
                  superset (within the structure matching tolerance)
  
          Returns:
              numpy array such that superset.sites[mapping] is within matching
              tolerance of subset.sites or None if no such mapping is possible