python解决给一个字符串，里面只会出现正整数以及 +-* 四种符号以及空格。已知这个字符串一定是符合算式规范的

给一个字符串，里面只会出现正整数以及 +-*/ 四种符号以及空格。已知这个字符串一定是符合算式规范的

import copy def test(demo_str): # 剔除空格 demo_str = demo_str.replace(' ', '') # 如果只有一个数字直接输出 if len(demo_str) == 1: print(demo_str) # 提取算术符与数字 number = [int(demo_str[x]) for x in range(len(demo_str)) if x % 2 == 0] suanshu = [demo_str[x] for x in range(len(demo_str)) if x % 2 == 1] # 进行深拷贝，防止数据混乱 number_new = copy.deepcopy(number) suanshu1 = copy.deepcopy(suanshu) while True: # 笨办法，每次先进行一次乘法或除法，在跟新数据和符号。 for i in range(len(suanshu)): if suanshu[i] == "*": number_new[i]=number[i] * number[i + 1] number_new.remove(number[i + 1]) suanshu1.remove("*") number = copy.deepcopy(number_new) suanshu = copy.deepcopy(suanshu1) break if suanshu[i] == "/": number_new[i]=number[i] // number[i + 1] number_new.remove(number[i + 1]) suanshu1.remove("/") number = copy.deepcopy(number_new) suanshu = copy.deepcopy(suanshu1) break number = copy.deepcopy(number_new) suanshu = copy.deepcopy(suanshu1) # 如果没有乘除，跳出循环。 if "*" not in suanshu1 and "/" not in suanshu1: break number_new1 = copy.deepcopy(number_new) suanshu2 = copy.deepcopy(suanshu1) while True: # 运算加减，每次运算，赋值给第一个数，循环计算完毕。 if suanshu1[0] == "+": number_new1[0] = number_new[0]+number_new[1] number_new1.remove(number_new[1]) suanshu2.remove("+") if suanshu1[0] == "-": number_new1[0] = number_new[0]-number_new[1] number_new1.remove(number_new[1]) suanshu2.remove("-") number_new = copy.deepcopy(number_new1) suanshu1=copy.deepcopy(suanshu2) if len(suanshu2) == 0: break print(number_new[0]) test('1+2*3+5/5+ 8*7-5-8')