func_code: def swap_unique_keys_values(d):
      new_d = {}
      seen = []
      for v in list(d.values()):
          if v not in seen:
              seen.append(v)
          elif v in seen:
              seen.remove(v)
      for k, v in list(d.items()):
          if v in seen:
              new_d[v] = k
      return new_d