dates = [['2017', '01', '15'], ['2017', '01', '14'], ['2017', '01', '13']]
for date in dates:
    date_cand = datetime.date(*map(int, date))
print((date_cand, (datetime.date.today() - date_cand).days))
date_cand = datetime.datetime.strptime('-'.join(date), '%Y-%m-%d')
print((date_cand, (datetime.date.today() - date_cand.date()).days))
List elements to time format and calculate the time diff from today