任意输入含加减乘除乘方开方的文本数学表达式，能检查语法错误，并计算结果

import re
import sys
import math

def get_priority(op):
    if op in ['*', '/']:
        return 2
    elif op == '**':
        return 3
    else:
        return 1

def get_op(op):
    if op == '+':
        return lambda x, y: x + y
    elif op == '-':
        return lambda x, y: x - y
    elif op == '*':
        return lambda x, y: x * y
    elif op == '/':
        return lambda x, y: x / y
    elif op == '**':
        return lambda x, y: x ** y
    elif op == 'sqrt':
        return lambda x: math.sqrt(x)

def cal(s):
    sl = re.split(r'([()+\-*/])', s)
    while '' in sl:
        sl.remove('')
    num = []
    op = []
    for i in sl:
        if i in ['(',