code: def _lhs(self, item):
          
          lhs = self.lhs
          if isinstance(self.lhs, (Op, Func)):
              lhs = self.lhs.expr(item)
          elif isinstance(self.lhs, six.string_types):
              try:
                  lhs = item.attrs[self.lhs].cast_value
              except Exception:
                  pass
  
          return lhs
docs: :type item: moto.dynamodb2.models.Item