How to reuse an app created in one Django project in another Django project

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Table of Contents

• Reusing an app created in one Django project in another Django project
  • Copying an application from one Django project into another
• Copying the polls app into a new top level directory called cast-votes
• Configuring the polls app in cast-votes
• Conclusion
• Related Resources
• Related Posts

Reusing an app created in one Django project in another Django project

I have created enough Django apps at this point that can be
reusable in other Django projects other than the ones they were
initially created in. It is smart and efficient development to be
able to do so. Why re-create something which already exists
somewhere else? This is a great path to creating reusable apps that
others can also use in their Django projects. It also paves a path
to writing great documentation for these apps.

Copying an application from one Django project into another

Following the
"Writing your first Django app"
series, I created a project called django_polls inside a top level
directory called django-polls. This was all fine. The app was
standalone, and that was great. But the problems began when I found
out about the Django advanced tutorial called
"Advanced tutorial: How to write reusable apps".
I approached the django_polls project like I would any other with the
naming. I did not know what was coming up next, and neither was
I appraised of it beforehand.

In this post, I will discuss how to avoid as muchas possible
such naming conflicts whilestill naming projects and reusable apps
with professional sounding names.

Copying the polls app into a new top level directory called cast-votes

I arbitrarily named anew top level directory cast-votes, and inside
I created a new project called config. I came across a number of
posts and threads where Django developers repeatedly called their
projects "config" so that there would be less of a chance of
naming conflicts when installing reusable apps. I thought it a
great idea, and decided to do the same for the purpose of this post.
It looks like I might continue to follow this convention!

You can follow the steps to creating a new project in my post
entitled
Creating the official Django Polls app Part 1.
However, this time, instead of creating a top level directory called
django-polls, and then a project called django_polls, create a top
level directory called cast-vote and a project called config inside
cast-vote.

If you have already completed the
Creating the official Django Polls app
series and therefore created an app called polls, you can copy the
polls app directory into the root of the cast-votes directory. There
should be no conflicts, since the project name does not contain
"polls" in it. It's as generic as it can get. We are not thinking
about creating a package from polls yet. That will take place in
another post. Right now we just want to make sure that our polls app
can be reused by ourselves on our local machine.

Configuring the polls app in cast-votes

Once we have placed polls inside the top level cast-votes directory,
we need to configure it a bit. The steps are not dissimilar from those
we were supposed to take to prepare our polls app package in the
"Advanced tutorial: How to write reusable apps".

First, we have to add polls to INSTALLED_APPS in config/settings.py:

INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
    "polls",
]

Next, we have to configure our polls.urls in config/urls.py:

from django.contrib import admin
from django.urls import include, path # include is new

urlpatterns = [
    path("polls/", include("polls.urls")), # new
    path("admin/", admin.site.urls),
]

Then, just make sure that there isn't anything in your templates that
does not belong in cast-votes. I had a couple of URLs in
templates/includes and templates/polls/index.html. Those URLS assumed
that I still hadanother reusable app called pages, which exists in
the original django-polls top level directory along with the
django_polls project. But since I haven't added this pages reusable
app to cast-votes, I had to make sure to update them. If, however,
I did want to add that reusable app so that I would have a top
level index page (because right now I don't and neither should you unless you
did something different), then I could keep those URLs which were
specific to django-polls/pages. There were no other "dependencies" on
django-polls.

If I were to package this app and publish it, those URLs would
cause a problem. The other question to ask is, do we want to
include templates in our packaged app or not? A packaged app is
going to be different from a reusable app which we created locally on
our machine and then copied over to another Django project. We have
some control over its behavior in relation to the project, and in
relation to other reusable apps which might be subsequently added.

According to a thread on stackoverflow entitled
Customize templates in a third party Django app,

You can put the template in a separate app within your project. Django looks
for templates in your apps in the order they are defined in INSTALLED_APPS,
and uses the first match: The order of INSTALLED_APPS is significant! For
example, if you want to customize the Django admin, you might choose to
override the standard admin/base_site.html template, from
django.contrib.admin, with your own admin/base_site.html in myproject.polls.
You must then make sure that your myproject.polls comes before
django.contrib.admin in INSTALLED_APPS, otherwise django.contrib.admin’s will
be loaded first and yours will be ignored.

This led me to the updated documentation for Django 5.1 entitled
How to override templates:

In your project, you might want to override a template in another Django
application, whether it be a third-party application or a contrib application
such as django.contrib.admin. You can either put template overrides in your
project’s templates directory or in an application’s templates directory.

And then:

.So create an app, called e.g. social_share_templates, and put it in
INSTALLED_APPS before django_social_share. Then add the template to this folder:

{{project_root}}/social_share_templates/templates/django_social_share/templatetags/post_to_facebook.html

And then:

The reason your current configuration does not work, is that your local app
has the same name as the app in site-packages. If your local app is an actual
python module, you won't be able to use the app in site-packages. Otherwise,
Django just looks for the templates in the app in site-packages.

And then:

So create an app, called e.g. social_share_templates, and put it in
INSTALLED_APPS before django_social_share. Then add the template to this
folder:

This issue(s) in the above thread is similar to what I encountered
when trying to package an existing reusable app following
Creating the official Django Polls app,
among other things.

If you have app and project templates directories that both contain
overrides, the default Django template loader will try to load the
template from the project-level directory first. In other words,
DIRS is searched before APP_DIRS.

To learn more about this, please visit
How to override templates
in the current Django (5.1) documentation.

We choose third party packages primarily for their
functionality/features. If we want to change the looks a bit, we
customize the templates, following the steps described in
How to override templates.

But in my case, I just made a couple of adjustments to fit the
app (module, not package) to the new config project.

To see the original django-polls structure containing both the pages
reusable app and polls reusable app, please visit
django-polls on Github.

Conclusion

In this post, I discussed how I can reuse an app created in one
Django project in another project so that I don't have to
"re-create" it all over again in another project.

Related Resources

• Writing your first Django app, part 1: Django documentation
• How to override templates: Django documentation
• Advanced tutorial: How to write reusable apps: Django documentation
• Customize templates in a third party Django app: stackoverflow

Related Posts

• Creating the official Django Polls app table of contents: mariadcampbell.com