python f.write中文乱码怎么解决

#coding:utf-8

s = u'中文'

f = open("test.txt","w")

f.write(s)

f.close()

#coding:utf-8

s = u'中文'

f = open("test.txt","w")

f.write(s.encode("utf-8"))

f.close()

#coding:utf-8

import sys

reload(sys)

sys.setdefaultencoding('utf-8')

s = u'中文'

f = open("test.txt","w")

f.write(s)

f.close()