def trim(n):
    if not isinstance(n, str):
        raise TypeError('只接受str类型')    _len = len(n)
    if _len == 0:
        return n
    elif n == ' ' * _len:
        return ''
    while n[0] == ' ':
        n = n[1:]
    while n[-1] == ' ':
        n = n[:-1]
    return n