action_precond_section : ACTION_PRECONDITIONS LCURLY action_precond_list RCURLY SEMI
                                  | ACTION_PRECONDITIONS LCURLY RCURLY SEMI

def p_action_precond_section(self, p):
        '''action_precond_section : ACTION_PRECONDITIONS LCURLY action_precond_list RCURLY SEMI
                                  | ACTION_PRECONDITIONS LCURLY RCURLY SEMI'''
        if len(p) == 6:
            p[0] = ('preconds', p[3])
        elif len(p) == 5:
            p[0] = ('preconds', [])
        self._print_verbose('action-preconditions')