利用切片操作，实现一个trim()函数，去除字符串首尾的空格，注意不要调用str的strip()方法：

 1 # -*- coding: utf-8 -*-
 2 def trim(s):
 3     if 0==len(s):
 4         return s
 5         
 6     while ‘ ‘==s[0]:
 7         s=s[1:]
 8         if 0==len(s):
 9             return s
10             
11     while ‘ ‘==s[-1]:
12         s=s[:-1]
13         if 0==len(s):
14             return s
15             
16     return s

 1 # 测试:
 2 from trim import trim
 3 if trim(‘hello  ‘) != ‘hello‘:
 4     print(‘测试失败!‘)
 5 elif trim(‘  hello‘) != ‘hello‘:
 6     print(‘测试失败!‘)
 7 elif trim(‘  hello  ‘) != ‘hello‘:
 8     print(‘测试失败!‘)
 9 elif trim(‘  hello  world  ‘) != ‘hello  world‘:
10     print(‘测试失败!‘)
11 elif trim(‘‘) != ‘‘:
12     print(‘测试失败!‘)
13 elif trim(‘    ‘) != ‘‘:
14     print(‘测试失败!‘)
15 else:
16     print(‘测试成功!‘)