def trim(s):    while len(s) >= 1 and s[0] == ' ':        s = s[1:]    while len(s) >= 1 and s[-1:] == ' ':        s = s[:-1]    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!')