f = open("yesterday","r",encoding="utf-8")
f_new=open("yesterday2.bak","w",encoding="utf-8")
for line in f:
if "等待我最喜爱的歌" in line:
line = line.replace("等待我最喜爱的歌","等待Alex最喜爱的歌")
f_new.write(line)
f.close() #要注意跳出for循环再close，否则会报错
f_new.close()
原文：http://www.cnblogs.com/xiaobai005/p/7805881.html