https://blog.ef67daisuki.club/2017/04/%e3%81%aa%e3%82%93%e3%81%8b%e4%ba%ba%e6%b0%97%e3%81%aefopen_s%e9%96%a2%e6%95%b0%e3%81%ab%e3%81%a4%e3%81%84%e3%81%a6/