import re# 格式化字符串函数(消除一些错误的格式)def format_string(string):# 一系列的替换语句string = string.replace("--", "-")string = string.replace("-+", "-")string = string.replace("++", "+")string = string.replace("*+", "*")string = string.replace("/+", "/")string = string.replace(" ", "-")return string# 检查函数（检查输入的表达式是否合法）def chek_expression(string):check_result = True # 标志位if not string.count("(") == string.count(")"): # 检查括号是否完整print("输入错误，未匹配到完整括号!")check_result = Falseif re.findall('[a-pr-z]+', string.lower()): # 检查是否包含字母print("输入错误，包含非法字符!")check_result = Falsereturn check_result# 加减法函数def add_minus(string):add_regular = r'[\-]?\d+\.?\d*\+[\-]?\d+\.?\d*' # 定义一个匹配的规则sub_regular = r'[\-]?\d+\.?\d*\-[\-]?\d+\.?\d*' # 同上# 注解：[\-]? 如果有负号，匹配负号； \d+ 匹配最少一个数字； \.? 是否有小数点，有就匹配；\d* 是否有数字有就匹配# \+ 匹配一个加号； [\-]?\d+\.?\d* 这几个同上# 加法while re.findall(add_regular, string): # 按照regular规则获取一个表达式,用while循环，把所有加法都算完add_list = re.findall(add_regular, string)for add_stars in add_list:x, y = add_stars.split('+')# 获取两个做加法的数(以+号作为分割对象)，分别赋给x和yadd_result = '+' + str(float(x) + float(y))string = string.replace(add_stars, add_result) # 替换string = format_string(string)# 减法while re.findall(sub_regular, string): # 用while循环，把所有减法都算完sub_list = re.findall(sub_regular, string)for sub_stars in sub_list:x, y = sub_stars.split('-') # 获取两个做减法的数(以-号作为分割对象)，分别赋给x和ysub_result = '+' + str(float(x) + float(y))string = string.replace(sub_stars, sub_result) # 替换string = format_string(string)return string# 乘、除法函数def multiply_divide(string):regular = r'[\-]?\d+\.?\d*[*/][\-]?\d+\.?\d*' # 定义一个匹配的规则regularwhile re.findall(regular, string):expression = re.search(regular, string).group() # 按照regular规则获取一个表达式# 如果是乘法if expression.count('*') == 1:x, y = expression.spilt('*')mul_result = str(float(x) * float(y))string = string.replace(expression, mul_result) # 计算结果替换原表达式string = format_string(string) # 格式化# 如果是除法if expression.count('/') == 1:x, y = expression.spilt('/')div_result = str(float(x) / float(y))string = string.replace(expression, div_result)string = format_string(string) # 格式化# 如果是阶乘if expression.count('**') == 1:x, y = expression.spilt('**')pow_result = 1for i in range(int(y)):pow_result *= int(x)string = string.replace(expression, str(pow_result))string = format_string(string) # 格式化return string# 主程序while True:source = input("请输入表达式：") # 输入要计算的式子if source == "Q": # 该判断语句只能写在前面，写后面会报错exit() # 如果输入是Q，退出elif chek_expression(source):print("eval result: ", eval(source)) # eval() 是把其他类型转换为字符串sourse = format_string(source)if source.count("(") > 0:stars = re.search(r'\([^()]*\)', source).group() # 去括号，得到括号里的字符串replace_stars = multiply_divide(stars) # 将括号的表达式进行乘除运算replace_stars = add_minus(stars) # 将乘除的结果进行加减运算source = format_string(source.replace(stars, replace_stars)) # 用计算结果替换括号字符串# 没有括号直接进行运算else:replace_stars = multiply_divide(source) # 乘除运算replace_stars = add_minus(source) # 加减运算source = source.replace(source, replace_stars)
