code: def index(self, value, start=None, stop=None):
          
          return self._list.index(value, start, stop)
docs: Return the smallest *k* such that `keysview[k] == value` and `start <= k
          < end`.  Raises `KeyError` if *value* is not present.  *stop* defaults
          to the end of the set.  *start* defaults to the beginning.  Negative
          indexes are supported, as for slice indices.