栈 后缀表达式

看了老师给的博客，学习了一下，我学的确实很菜啊，仿照写了一个可以实现任意数字个数的加括号运算，目前只支持加一个括号。。。。

收获真的挺大

def to_rpn(f4):
    def compare(x, y):
        v = {'+': 0, '-': 0, '*': 1, '/': 1, '(': 2}
        return 1 if y == '(' else v[x] - v[y]
    rpn, operators = [], []
    for i in f4:
        if i not in ['+', '-', '*', '/', '(', ')']:
            rpn.append(i)
        else:
            if i == ')':
                while operators[-1] != '(':
                    rpn.append(operators.pop())
                operators.pop()
            elif not operators or 0 < compare(i, operators[-1]):
                operators.append(i)
            else:
                while operators and compare(i, operators[-1]) < 1:
                    rpn.append(operators.pop())
                operators.append(i)
    while operators:
        rpn.append(operators.pop())
    return rpn
def rpn_to_answer(f4):
    answer_func = [lambda x, y: x + y, lambda x, y: x - y, lambda x, y: x * y, lambda x, y: x / y]
    answer_func_re = [lambda x, y: y + x, lambda x, y: (y - x) * -1, lambda x, y: y * x]
    number = []
    for i in f4:
        if i not in ['+', '-', '*', '/']:
            number.append(i)
        else:
            x, y, z = number.pop(), number.pop(), None
            try:
                z = answer_func[['+', '-', '*', '/'].index(i)](y, x)
            except TypeError:
                z = answer_func_re[['+', '-', '*', '/'].index(i)](y, x)
            number.append(z)
    return number[0]
def random_f4(_op):#操作数
    from random import randint as ran
    r = []
    j = _op*2 - 1
    for i in range(j):
        if i % 2 == 1:
            r.append(['+', '-', '*', '/'][ran(0, 3)])
        if i % 2 == 0:
            r.append(ran(1, 9))
    x = ran(0,_op-2)
    r.insert(x*2,'(')
    y = ran(x+2,_op)
    r.insert(y*2,')')

    return (r)
if __name__ == "__main__":
    from fractions import Fraction as F
    ops = input("数字个数：")
    ops = int(ops)
    r = random_f4(_op=ops)
    print(r)
    r = to_rpn(r)
    print(r)
    r = rpn_to_answer(r)
    r = F(r).limit_denominator(1000)
    print(r)

截图：

 

现在python学的还是很菜啊。。。。。。。。。