argument_list : assignment_expr
                         | argument_list COMMA assignment_expr

def p_argument_list(self, p):
        """argument_list : assignment_expr
                         | argument_list COMMA assignment_expr
        """
        if len(p) == 2:
            p[0] = [p[1]]
        else:
            p[1].append(p[3])
            p[0] = p[1]