Quickly select a random model from a Django queryset

gistfile1.py

import random

def fast_random_model(callback, queryset):
    """ Attempts to quickly retrieve a single randomly selected object from a
        queryset, then passes it to the callback if successful. """

    # This implementation avoids using `order by random()` which is notoriously
    # slow with large tables in Postgres.

    count = queryset.count()

    try:
        random_index = random.randint(0, count - 1)
    except ValueError:
        pass # The queryset was empty.
    else:
        try:
            model = queryset[random_index]
        except IndexError:
            pass # Failed due to the race condition above.
        else:
            callback(model)