Python利用切片操作，实现一个trim()函数，去除字符串首尾的空格

def trim(s):
    if len(s) == 0:
        return s
    else:
        while len(s) > 0:
            if s[0] == ' ':
                s = s[1:]
            elif s[-1] == ' ':
                s = s[:-1]
            elif s[0] != ' ' and s[-1] != ' ':
                break
    return s
        

# 测试:
if trim('hello  ') != 'hello':
    print('测试失败!')
elif trim('  hello') != 'hello':
    print('测试失败!')
elif trim('  hello  ') != 'hello':
    print('测试失败!')
elif trim('  hello  world  ') != 'hello  world':
    print('测试失败!')
elif trim('') != '':
    print('测试失败!')
elif trim('    ') != '':
    print('测试失败!')
else:
    print('测试成功!')