How to revert the last migration

Concatenating the querysets into a list is the simplest approach. If the database will be hit for all querysets anyway (e.g. because the result needs to be sorted), this won't add further cost.

from itertools import chain
result_list = list(chain(page_list, article_list, post_list))

Using itertools.chain is faster than looping each list and appending elements one by one, since itertools is implemented in C. It also consumes less memory than converting each queryset into a list before concatenating.

Now it's possible to sort the resulting list e.g. by date (as requested in hasen j's comment to another answer). The sorted() function conveniently accepts a generator and returns a list:

result_list = sorted(
    chain(page_list, article_list, post_list),
    key=lambda instance: instance.date_created)

If you're using Python 2.4 or later, you can use attrgetter instead of a lambda. I remember reading about it being faster, but I didn't see a noticeable speed difference for a million item list.

from operator import attrgetter
result_list = sorted(
    chain(page_list, article_list, post_list),
    key=attrgetter('date_created'))

One solution that I have employed is to do this:

1) Create a custom management command, e.g.

python manage.py my_cool_command

2) Use cron (on Linux) or at (on Windows) to run my command at the required times.

This is a simple solution that doesn't require installing a heavy AMQP stack. However there are nice advantages to using something like Celery, mentioned in the other answers. In particular, with Celery it is nice to not have to spread your application logic out into crontab files. However the cron solution works quite nicely for a small to medium sized application and where you don't want a lot of external dependencies.

EDIT:

In later version of windows the at command is deprecated for Windows 8, Server 2012 and above. You can use schtasks.exe for same use.

**** UPDATE **** This the new link of django doc for writing the custom management command