code: def swap(self, i, j):
  		
  		i = self._fix_neg_index(i)
  		j = self._fix_neg_index(j)
  		self._list[i], self._list[j] = self._list[j], self._list[i]
  		self._dict[self._list[i]] = i
  		self._dict[self._list[j]] = j
docs: Swap the values at indices i & j.
  
  		.. versionadded:: 1.1