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)