code: def insert(self, index, object):
          
          self._check(object.id)
          list.insert(self, index, object)
          # all subsequent entries now have been shifted up by 1
          _dict = self._dict
          for i, j in iteritems(_dict):
              if j >= index:
                  _dict[i] = j + 1
          _dict[object.id] = index
docs: insert object before index