import re def format_string(s): # 对表达式进行格式化 s = s.replace(' ', '') s = s.replace("--", "+") s = s.replace("++", "+") s = s.replace("+-", "-") s = s.replace("*+", "*") s = s.replace("/+", "/") return s def check_expression(s): # 对表达式进行检测 flag = True if not s.count("(") == s.count(")"): print("括号没有闭合") flag = False if re.findall('[a-z]+', s.lower()): print("有非法字符") flag = False return flag def calc_mul_div(s): regular = '[\-]?\d+\.?\d*[*/][\-]?\d+\.?\d*' while re.findall(regular, s): expression = re.search(regular, s).group() if expression.count("*"): # 判断是否是乘法 x, y = expression.split("*") mul_result = str(float(x) * float(y)) s = s.replace(expression, mul_result) s = format_string(s) if expression.count("/"): # 判断是否是除法 x, y = expression.split('/') div_result = str(float(x) / float(y)) s = s.replace(expression, div_result) s = format_string(s) return s def calc_add_sub(s): # 判断加减法 add_regular = '[\-]?\d+\.?\d*\+[\-]?\d+\.?\d*' sub_regular = '[\-]?\d+\.?\d*\-[\-]?\d+\.?\d*' while re.findall(add_regular, s): add_list = re.findall(add_regular, s) for add_str in add_list: x, y = add_str.split("+") add_result = "+" + str(float(x) + float(y)) s = s.replace(add_str, add_result) s = format_string(s) while re.findall(sub_regular, s): sub_list = re.findall(sub_regular, s) for sub_str in sub_list: numbers = sub_str.split("-") if len(numbers) == 3: # 如果表达式类似 -1-1,则 list 是 ['', '1', '1'] , # 如果表达式类似 8-2, 则 list 是 ['8', '2'] result = 0 for v in numbers: if v: result -= float(v) else: x, y = numbers result = float(x) - float(y) s = s.replace(sub_str, "+" + str(result)) s = format_string(s) return s if __name__ == "__main__": s = '(( 2 /1 * 7 ) - ( 3 *4 ) )' if check_expression(s): s = format_string(s) while s.count("(") > 0: strs = re.search('\([^()]*\)', s).group() replace_str = calc_mul_div(strs) replace_str = calc_add_sub(replace_str) s = format_string(s.replace(strs, replace_str[1:-1])) # 去掉多余的括号 else: replace_str = calc_mul_div(s) replace_str = calc_add_sub(replace_str) s = s.replace(s, replace_str) print("result: ", s.replace("+", "")) 运行结果： result: 2.0 文章来源: Python 练习: 计算器