code: def _hashed_indexing_key(self, key):
          
          from pandas.core.util.hashing import hash_tuples, hash_tuple
  
          if not isinstance(key, tuple):
              return hash_tuples(key)
  
          if not len(key) == self.nlevels:
              raise KeyError
  
          def f(k, stringify):
              if stringify and not isinstance(k, str):
                  k = str(k)
              return k
          key = tuple(f(k, stringify)
                      for k, stringify in zip(key, self._have_mixed_levels))
          return hash_tuple(key)
docs: validate and return the hash for the provided key
  
          *this is internal for use for the cython routines*
  
          Parameters
          ----------
          key : string or tuple
  
          Returns
          -------
          np.uint64
  
          Notes
          -----
          we need to stringify if we have mixed levels