Django management command: provide base class without circular reference

Question

First off, it is not about circular Model references. I could find a lot of answers about those.

I am building an app that let's you easily define reminders in your settings. Therefore the REMINDERS setting looks like this:

settings

REMINDERS = [
    {
        'reminder_id': 'my-id',
        'reminder_class': 'students.reminders.ExpiredAvailabilityEmailReminder',
    },
]

In this app (reminders), I provide a base class for these reminders, that has some default behaviour in it. To define a reminder, the only thing I have to do is for example:

students_app/reminders.py

from reminders.base_reminders import ReminderEmail
from .models import Student


class ExpiredAvailabilityEmailReminder(ReminderEmail):
    template_name = 'students/emails/setting_expired.html'

    def get_queryset(self):
        return Student.objects.filter(
                    is_active=True,
                    setting_expired__lt=datetime.date.today())

reminders_app/management/commands/send_reminders.py

The management command imports this reminder_class-string in handle with django.utils.module_loading.import_by_path, but this fails with:

django.core.exceptions.ImproperlyConfigured: Error importing module studenten.reminders: "No module named base_reminders"

Because it becomes a circular reference. How can I provide the users of my app with an subclassable base class, without running into this problem?

Thanks.

Answer 1

This problem relates to the default import order in Python 2. If you are in students_app/reminders.py and you have from reminders.base_reminders import ReminderEmail it isn't clear whether the reminders module is referring to itself or your app which is also called reminders. To fix this you can use from __future__ import absolute_import in Python 2.5+ (or use Python 3 where this is the default)

from __future__ import absolute_import
from reminders.base_reminders import ReminderEmail

which will ensure that the reminders import uses the reminders app rather than the relative reminders module.

The other fix is a documentation one which is to not encourage people to name their module reminders to avoid this naming conflict.