#! /usr/bin/env python3import sys
import redef welcome_func():flag_exit = Truewelcome_str = "超级计算器"print(welcome_str.center(50, "*"), '\n')while flag_exit:exp = input("请输入要计算的表达式[q:退出]: ").strip()if exp == "q":flag_exit = Falseelif len(exp) == 0:continueelse:exp = re.sub("\s*", '', exp)     ## 取出空格return expdef multi_divide(expression):val = re.search("\d+\.?\d*[*/][+-]?\d+\.?\d*", expression)    ##匹配乘除号，如192.168*-1.99if not val:    # 乘除号不存在，返回输入的表达式return expressiondata = re.search("\d+\.?\d*[*/][+-]?\d+\.?\d*", expression).group()if len(data.split('*')) > 1:           # 当可以用乘号分割，证明有乘法运算part1, part2 = data.split('*')     # 用除号分割value = float(part1) * float(part2)else:part1, part2 = data.split('/')if float(part2) == 0:            # 如果分母为0，则退出计算sys.exit("计算过程中有被除数为0的存在，计算表达式失败！")value = float(part1) / float(part2)s1, s2 = re.split("\d+\.?\d*[*/][+-]?\d+\.?\d*", expression, 1)  # 分割表达式next_expression = "%s%s%s" % (s1, value, s2)return multi_divide(next_expression)      # 递归表达式def add_sub(expression):expression = expression.replace('+-', '-')      # 替换表达式里的所有‘+-‘expression = expression.replace('--', '+')      # 替换表达式里的所有‘--‘expression = expression.replace('-+', '-')      # 替换表达式里的所有‘-+‘expression = expression.replace('++', '+')      # 替换表达式里的所有‘++‘
data = re.search('\d+\.?\d*[+-]\d+\.?\d*', expression)    # 匹配加减号if not data:                    # 如果不存在加减号，则证明表达式已计算完成，返回最终结果return expressionval = re.search('[+-]?\d+\.?\d*[+-]\d+\.?\d*', expression).group()if len(val.split('+')) > 1:                   # 以加号分割成功，有加法计算part1, part2 = val.split('+')value = float(part1) + float(part2)elif val.startswith('-'):                     # 如果是已‘-‘开头则需要单独计算part1, part2, part3 = val.split('-')value = -float(part2) - float(part3)      # 计算以负数开头的减法else:part1, part2 = val.split('-')value = float(part1) - float(part2)s1, s2 = re.split('[+-]?\d+\.?\d*[+-]\d+\.?\d*', expression, 1)    # 分割表达式next_expression = "%s%s%s" % (s1, value, s2)return add_sub(next_expression)              # 递归运算表达式def del_bracket(expression):## [^()]+  匹配除了括号以外的任意字符if not re.search(r"\([^()]+\)", expression):   # 判断小括号，如果不存在小括号，直接调用乘除，加减计算ret1 = multi_divide(expression)ret2 = add_sub(ret1)return ret2                      # 返回最终计算结果data = re.search(r"\([^()]+\)", expression).group()    # 如果有小括号，匹配出优先级最高的小括号print("获取表达式", data)data = data.strip('[\(\)]')           # 剔除小括号ret1 = multi_divide(data)# print("全部乘除计算完后的表达式：", ret1)ret2 = add_sub(ret1)# print("全部加减计算结果：", ret2)part1, part2 = re.split(r"\([^()]+\)", expression, 1)         # 分割表达式expression = "%s%s%s" % (part1, ret2, part2)return del_bracket(expression)                         # 递归去小括号if __name__ == "__main__":try:expression = welcome_func()     ## 获取表达式print(expression)result = eval(expression)       ## 用eval来验证print(result)ret = del_bracket(expression)   ## 用函数计算得出结果result = float(result)ret = float(ret)print("eval计算结果: ", result)print("表达式计算结果: ", ret)except (SyntaxError, ValueError, TypeError):print("输入表达式不合法，请检查！")