实现栈的表达式的转化

from stack_set import Stackdef infixToPostfix(infixpr): pre={} pre['*'],pre['/']=3,3 pre['+'],pre['-']=2,2 pre['(']=1 charlist=[chr(i) for i in range(65,91)] numlist=[i for i in range(10)] opstack=Stack() postfixlist=[] items=infixpr.split() for item in items: if item in charlist or item in numlist: postfixlist.append(item) elif item=="(": opstack.push(item) elif item==')': tokentop=opstack.pop() while tokentop!="(": postfixlist.append(tokentop) tokentop=opstack.pop() else: while(not opstack.isEmpty()) and (pre[item]<=pre[opstack.peek()]): postfixlist.append(opstack.pop()) opstack.push(item) print("stack:{},postlist:{}".format(opstack.items,postfixlist)) while not opstack.isEmpty(): postfixlist.append(opstack.pop()) return "".join(postfixlist)if __name__ == '__main__': infix="A + ( B * C )" postfix=infixToPostfix(infix) print("其对应的后缀表达式：{}".format(postfix))