get_date_tree.py

def get_date_tree():
    """
    Get all dates with stories, store in Redis. Cached for 1 day.

    Returns an OrderedDict, with datetime objects as keys.

    OrderedDict([(
        datetime.date(1963, 1, 1), OrderedDict([(
            datetime.date(1963, 11, 1), [
                datetime.date(1963, 11, 22),
                datetime.date(1963, 11, 23),
                datetime.date(1963, 11, 24)
            ]
        )])
    )])

    Think of it more like a regular dict:
    date_tree = {
        datetime.date(1963, 1, 1): {
            datetime.date(1963, 11, 1): [
                datetime.date(1963, 11, 22),
                datetime.date(1963, 11, 23),
                datetime.date(1963, 11, 24)
            ]
        }
    }

    Access it like a normal dict, with datetimes as keys:

    To get all the months in in 1963:
        >>date_tree = get_date_tree()
        >>months = date_tree[date(1963,1,1)].keys()

    To get all the days in November, 1963:
        >>date_tree = get_date_tree()
        >>days = date_tree[date(1963,1,1)][date(1963,11,1)]

    """

    key = "date_tree"
    try:
        date_tree = get_redis_cache(key)
    except:
        date_tree = None

    if not date_tree:
        all_dates = Story.live_objects.all().dates('pubdate', 'day').distinct()
        date_tree = OrderedDict()
        for dt in all_dates:
            # create a tree of all dates, keys are datetime objects
            date_tree.setdefault(
                date(dt.year, 1, 1), OrderedDict()).setdefault(
                    date(dt.year, dt.month, 1), []).append(dt.date())
        set_redis_cache(key, date_tree, expires=86400)  # expire key in 24 hours

    return date_tree