インメモリー ストリーム活用術
PyCon JP 2020
https://github.com/ftnext/PyConTalkSummary/issues/31
PNGをBytesIOで取り扱う例
https://speakerdeck.com/hayaosuzuki/how-to-use-in-memory-streams?slide=22
https://docs.python.org/ja/3/library/io.html#binary-i-o
（
Python io
）
f = io.BytesIO(b"some initial binary data: \x00\x01")