def trim(s):

    if not isinstance(s,str):

        raise TypeError('bad operand type')

    if s[0] == ' ' and s[-1] == ' ':

        return s[1:len(s)-1]

    elif s[0] == ' ':

        return s[1:]

    elif s[-1] == ' ':

        return s[:-1]

    else:

        return s