import re from functools import reduce ''' 分析：   1.用户输入   2.判断表达式是否正确   3.计算     1）通过正则获取（。。。）进行计算并替换（。。。）     2）循环1）直到未找到则标记为最后一层，计算结果并返回     计算中的注意事项：         注意两个数的前后位置，不要颠倒了         查找含有负数的符号，进行转换（查找负数符号最前面的-或+进行倒换，并去掉负数符号）   4.显示结果 ''' def count(first,symbol,second):     '''     计算两个数的运算值     :param first: 第一个数     :param symbol: 运算符     :param second: 第二个数     :return:     '''     if symbol == '*':         return float(first) * float(second)     elif symbol=='/':         return float(first) / float(second)     elif symbol=='+':         return float(first) + float(second)     elif symbol == '-':         return float(first) - float(second) def count_express(group):     '''     计算一个字符表达式的值     :param group: 要运算的字符     :return:     '''     result = re.findall('[0-9]+[.0-9]*|[^0-9]', group)     list1 = list(reversed(list(result)))     first = ''     symbol = '+'     second = '0'     first = list1.pop()     stack =[]     # '1+2*(2+3*4-4)'     if first == '-':         first += list1.pop()     while len(list1) != 0:         symbol = list1.pop()         second = list1.pop()         if symbol == '-' or symbol == '+':             stack.append(first)             stack.append(symbol)             first = second             continue         first = str(count(first, symbol, second))     while len(stack) > 1:         symbol = stack.pop()         second = stack.pop()         first = count(second, symbol, first)     return str(first) def group_count(express):     '''     计算表达式值     :param express: 字符表达式     :return:     '''     while True:         pattern = r'\([^()]+\)'         pat = re.compile(pattern)         group = pat.search(express)         result = []         # 判断是否找到（）         flag = True         if group != None:             group = group.group()             group = group.replace('(','').replace(')','')         else:             group = express             flag = False         result = count_express(group)         # 如果是最后一层，直接返回值         if flag is False:             return result         # 将express中找到(..)的运算结果进行替换         express = pat.sub(result,express)         express = replace_symbol(express)         print(express) def replace_symbol(express):     '''     将负数转正     :param express:     :return:     '''     split_list = re.split('[+*/-]-', express)     b = split_list[0]     # 字符反转     c = reduce(lambda x, y: y + x, b)     # 查找离要负号位最近是（+-）进行替换     d = re.search('[+-]', c)     f = d.group()     m = '+' if f == '-' else '-'     list_str = list(c)     list_str[d.span()[0]] = m     list_str.reverse()     c = ''.join(list_str)     return c +express[len(c)]+ split_list[1] def check_express(express):     '''     校验输入的表达式是否正确     :param express: 字符表达式     :return:     '''     pattern1 = '[^0-9+*/.()-]|[^0-9][+/*.]|[0-9][(]|^[+/*.]|[+/*.]$'     result = re.search(pattern1,express)     return result def input_express():     # express = input("请输入（只能包含0-9+-*/.（）字符）：")     express = '-1+2*3-4/(-10*2)-3'     express = re.sub(' ', '', express)     result = check_express(express)     if result != None:         span = str(result.span())         group = str(result.group())         print('输入了错误的字符或表达式格式不对，所在位置：%s，错误字符：%s' % (span, group))         sys.exit(0)     return express if __name__ == '__main__':     express = input_express()     result = group_count(express)     print('结果：%s' %result)