Python在往文件里写东西的时候，如果ascii码报错
参考
http://stackoverflow.com/questions/19833440/unicodeencodeerror-ascii-codec-cant-encode-character-u-xe9-in-position-7
You need to encode Unicode explicitly before writing to a file, otherwise Python does it for you with the default ASCII codec.
Pick an encoding and stick with it:
f.write(printinfo.encode('utf8') + '
')