code: def _fixIndex(self, index, truncate=False):
          
          assert not isinstance(index, slice), 'slices are not supported (yet)'
          if index < 0:
              index += self.length
          if index < 0:
              if not truncate:
                  raise IndexError('stored List index out of range')
              else:
                  index = 0
          return index
docs: @param truncate: If true, negative indices which go past the
                           beginning of the list will be evaluated as zero.
                           For example::
  
                           >>> L = List([1,2,3,4,5])
                           >>> len(L)
                           5
                           >>> L._fixIndex(-9, truncate=True)
                           0