code: def p_postfix_expr(self, p):
          
          if len(p) == 2:
              p[0] = p[1]
          else:
              p[0] = self.asttypes.PostfixExpr(op=p[2], value=p[1])
              p[0].setpos(p, 2)
docs: postfix_expr : left_hand_side_expr
                          | left_hand_side_expr PLUSPLUS
                          | left_hand_side_expr MINUSMINUS