```

import re

x = input('请输入你要计算的计算式：')   # 用户输入

# 判断用户输入的是否有字母，括号个数是否正确，同时处理字符串中的空格

if re.findall('[a-zA-Z]',x):

    print('输入错误，算式中出现字母！')

    exit()

if '(' in x or ')' in x:

    if x.count('(') != x.count(')'):

        print('输入错误，括号个数不正确！')

        exit()

if ' ' in x:

    x = x.replace(' ','')

# 定义一个处理乘法和除法的函数，在只有加减乘除的运算中，除法若是最优先运算的话，不会出错。

# 经过这个函数处理后，计算式中的 乘除法就处理完了，只剩下加减法了

def multiplication_division(calculate):

    # 在计算完括号里面的计算式时，如果得到一个负数，那么替换后会出现 '*-' '/-' '+-' '--' 这么几种情况，故函数先判断处理这种情况。

    while '*-' in calculate:

        if re.search('-[0-9.]+\*-',calculate):

            replace1 = re.search('-[0-9.]+\*-',calculate).group()

            replace = replace1.replace('*-','*')

            replace = replace.replace('-','+')

            calculate = calculate.replace(replace1,replace)

        elif re.search('\+[0-9.]+\*-',calculate):

            replace1 = re.search('\+[0-9.]+\*-', calculate).group()

            replace = replace1.replace('*-', '*')

            replace = replace.replace('+', '-')

            calculate = calculate.replace(replace1, replace)

    while '/-' in calculate:

        if re.search('-[0-9.]+/-',calculate):

            replace1 = re.search('-[0-9.]+/-',calculate).group()

            replace = replace1.replace('/-','/')

            replace = replace.replace('-','+')

            calculate = calculate.replace(replace1,replace)

        elif re.search('\+[0-9.]+/-',calculate):

            replace1 = re.search('\+[0-9.]+/-', calculate).group()

            replace = replace1.replace('/-', '/')

            replace = replace.replace('+', '-')

            calculate = calculate.replace(replace1, replace)

    while '/' in calculate:

        if re.findall('^-[0-9.]+/[0-9.]+',calculate):

            division = re.findall('-[0-9.]+/[0-9.]+',calculate)[0]

            result = re.findall('(-[0-9.]+)/([0-9.]+)',division)[0]

            result = float(result[0])/float(result[1])

            calculate = calculate.replace(division,str(result))

        else:

            division = re.findall('[0-9.]+/[0-9.]+',calculate)[0]

            result = re.findall('([0-9.]+)/([0-9.]+)',division)[0]

            result = float(result[0])/float(result[1])

            calculate = calculate.replace(division,str(result))

    while '*' in calculate:

        if re.findall('^-[0-9.]+\*[0-9.]+', calculate):

            multiplication = re.findall('-[0-9.]+\*[0-9.]+',calculate)[0]

            result = re.findall('(-[0-9.]+)\*([0-9.]+)',multiplication)[0]

            result = float(result[0])*float(result[1])

            calculate = calculate.replace(multiplication,str(result))

        else:

            multiplication = re.findall('[0-9.]+\*[0-9.]+', calculate)[0]

            result = re.findall('([0-9.]+)\*([0-9.]+)', multiplication)[0]

            result = float(result[0]) * float(result[1])

            calculate = calculate.replace(multiplication, str(result))

    return calculate

# 定义一个处理只有加减法的函数

def addition_subtraction(calculate):

    if '+-' in calculate:

        calculate = calculate.replace('+-','-')

    elif '--' in calculate:

        calculate = calculate.replace('--','+')

    list_number = []

    list_number_ = re.findall('[+-]?[0-9.]+',calculate)

    for i in list_number_:

        list_number.append(float(i))

    return sum(list_number)

# 找到最里面的括号，并传给前面的乘除法运算和加减法运算，得到最终的结果

def final(x):

    while '(' in x:

        process = re.findall('\(([^()]+)\)',x)

        for calculate in process:

            y = multiplication_division(calculate)

            y = addition_subtraction(y)

            x = x.replace('('+calculate+')',str(y))

    x = multiplication_division(x)

    return addition_subtraction(x)

print(final(x))

```