def check_parens(text) :

     # 括号匹配检查函数，text 是被检查的正文串

     parens = "(){}[]"

     open_parens = "({["

     opposite = {")":"(", "}":"{", "]":"["}

     def parentheses(text) :

         # 括号生成器，每次调用返回text里的下一括号及其位置

         i.text_len = 0,len(text)

         while True :

             while i < text_len and text[i] not in parens :

                 i += 1

             if i >= text_len :

                 return

             yield text[i],i

             i += 1

     st = SStack()  # 创建栈 st

     for pr , i in parentheses(text) :  # 对text里各括号和位置迭代

         if pr in open_parens :      # 开括号，压栈并继续

             st.push(pr)

         elif st.pop() != opposite[pr] :  # 闭括号 若匹配失败就退出

             print("Unmatching is found at ",i,"for",pr)

             return False

         # else :  匹配成功什么也不做