:param days: a positive integer.
    Return true if the adatetime is on the specified days ago

def is_days_ago(adatetime, days):
    """
    :param days: a positive integer.
    Return true if the adatetime is on the specified days ago
    """
    if days == 1:
        end_time = last_midnight()
        start_time = end_time - timedelta(days=1)
    else:
        start_time = last_midnight() - timedelta(days=days)
        end_time = start_time + timedelta(days=1)
    return start_time <= adatetime <= end_time