week4_day6(计算器)

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 # author by lh
 4 
 5 import re
 6 
 7 
 8 # 替换空格，++，--等符号
 9 def rep(s):
10     s = s.replace(‘ ‘, ‘‘)
11     s = s.replace(‘++‘, ‘+‘)
12     s = s.replace(‘+-‘, ‘-‘)
13     s = s.replace(‘--‘, ‘+‘)
14     return s
15 
16 
17 # 检查是否合法
18 def checkout(s):
19     flag = True
20     if re.findall(‘[a-zA-Z]‘, s):
21         print(‘您可能输入了字母或特殊字符，请重新输入！‘)
22         flag = False
23     return flag
24 
25 # 乘除运算
26 def mul_div(s):
27     while re.search(‘\d+\.?\d*[*/]-?\d+\.?\d*‘, s):  # 条件满足时，做乘除
28         ret = re.search(‘\d+\.?\d*[*/]-?\d+\.?\d*‘, s).group()  # 取出乘除表达式
29         x, y = re.split(‘[*/]‘, ret)  # 取出计算的值
30         if ‘*‘ in ret:
31             mul = float(x) * float(y)
32         elif ‘/‘ in ret:
33             mul = float(x) / float(y)
34         s = s.replace(ret, str(mul))  # 计算结果代替旧的表达式
35     return s
36 
37 # 加减运算
38 def add_minus(s):
39     while re.search(‘\d+\.?\d*[+-]\d+\.?\d*‘, s):
40         ret = re.search(‘\d+\.?\d*[+-]\d+\.?\d*‘, s).group()
41         x, y = re.split(‘[+-]‘, ret)
42         if ‘+‘ in ret:
43             add = float(x) + float(y)
44         elif ‘-‘ in ret:
45             add = float(x) - float(y)
46         s = s.replace(ret, str(add))
47         s = rep(s)
48     return s
49 
50 
51 str1 = input(‘请输入您要计算的表达式：‘)
52 str1 = rep(str1)
53 if checkout(str1):
54     while re.search(‘\(‘, str1):  # 找到最后一个括号
55         a = re.search(‘\([^()]+\)‘, str1).group()  # 找到最后一个括号中的表达式
56         n = re.sub(‘[()]‘, ‘‘, a)  # 去括号
57         a1 = mul_div(n)  # 计算乘除
58         str1 = rep(str1)
59         res = add_minus(a1)  # 计算加减
60         str1 = str1.replace(a, res)
61     else:
62         add = mul_div(str1)  # 没有括号时计算乘除
63         a2 = str1.replace(str1, add)  # 计算结果代替旧的表达式
64         str1 = rep(str1)
65         res = add_minus(a2)  # 计算加减
66         str1 = str1.replace(str1, res)
67         str1 = rep(str1)
68         str1 = add_minus(str1)
69 print(str1)
70 
71 print(eval(str1))