in2post.py

#==================================================
#==>      Title: 中缀 --> 后缀                         
#==>     Author: Zhang zhen                   
#==>      Email: hustmatnoble.gmail.com
#==>     GitHub: https://github.com/MatNoble
#==>       Date: 2/20/2021
#==================================================

# coding:utf-8
def priority(z):
    if z in ['×', '*', '/']:
        return 2
    elif z in ['+', '-']:
        return 1

def in2post(expr):
    """ :param expr: 中缀表达式
        :return: 后缀表达式

        Example：
            "1+((2+3)×4)-5"
            "1 2 3 + 4 × + 5 -"
    """
    stack = []  # 存储栈
    post  = []  # 后缀表达式存储
    for z in expr:
        if z not in ['×', '*', '/', '+', '-', '(', ')']:  # 数字直接输出
            post.append(z)
        else:
            if z != ')' and (not stack or z == '(' or stack[-1] == '('
                             or priority(z) > priority(stack[-1])):  # stack 不空；栈顶为（；优先级大于
                stack.append(z)     # 运算符入栈
            elif z == ')':  # 右括号出栈
                while True:
                    x = stack.pop()
                    if x != '(':
                        post.append(x)
                    else:
                        break
            else:   # 比较运算符优先级，看是否入栈出栈
                while True:
                    if stack and stack[-1] != '(' and priority(z) <= priority(stack[-1]):
                        post.append(stack.pop())
                    else:
                        stack.append(z)
                        break
    while stack:    # 还未出栈的运算符，需要加到表达式末尾
        post.append(stack.pop())
    return post

# if __name__ == '__main__':
s = "1+((2+3)×4)-5"
post = in2post(s)
print('后缀表达式： ',post)