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Neri.

#1 Created at ... [Delete] [Delete and Lock User]

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