日付－DOY間の変換
    Top > Python > 日付・時間
    DOY
    Day Of Year, その年の何日目に当たるか． 1月1日ならDOY=1, 2月3日ならDOY=34.
    DATE -> DOY
    DOY -> DATE
    References
    datetime - Convert Year/Month/Day to Day of Year in Python - Stack Overflow + https://stackoverflow.com/questions/620305/convert-year-month-day-to-day-of-year-in-python