def trim(s):
    # print('初始值：',s,len(s))
    if s=='':
        return ''
    if s and s[0:1]==' ':
        s=s[1:(len(s))]
    if s and s[-1]==' ':
        s=s[:(len(s)-2)]
    if s and (s[-1]!=' ')and(s[0:1]!=' '): 
        return s
    else:
        return trim(s)