Python Infix Calculator

import re
import operator

def main():
    op_stack = []

    val_stack = []

    ops = ['*', '/', '+', '-']

    precedence = { '*':3, '/':3, '+':2, '-':2, '(': 0}

    eval_string = input("Enter an expression: ")

    eval_string = eval_string.replace(" ", "")

    eval_string = re.split(r'([)(*/+-])', eval_string)

    operand = re.compile(r'\d+\.*\d*')

    for token in eval_string:

        if operand.match(token):
            val_stack.append(float(token))
            print(token)

        if token == '(':
            op_stack.append(token)

        if token in ops:
            while len(op_stack) > 0 and precedence[token] <= precedence[op_stack[-1]]:
                op = op_stack.pop()
                do_op(op, val_stack)

            op_stack.append(token)

        if token == ')':
            while len(op_stack) > 0 and op_stack[-1] != '(':
                op = op_stack.pop()
                do_op(op, val_stack)

            op_stack.pop()

    while len(op_stack) > 0:
            op = op_stack.pop()
            do_op(op, val_stack)

    print(val_stack.pop())

def do_op(op, val_stack):
    function = {'*':operator.mul, '/':operator.truediv, '+':operator.add, '-':operator.sub}
    temp = val_stack.pop()
    val_stack.append(function[op](val_stack.pop(), temp))

main()