docs/intro/reusable-apps.txt
=============================================
Advanced tutorial: How to write reusable apps
=============================================
This advanced tutorial begins where :doc:`Tutorial 8 </intro/tutorial08>`
left off. We'll be turning our web-poll into a standalone Python package
you can reuse in new projects and share with other people.
If you haven't recently completed Tutorials 1–7, we encourage you to review
these so that your example project matches the one described below.
Reusability matters
===================
It's a lot of work to design, build, test and maintain a web application. Many
Python and Django projects share common problems. Wouldn't it be great if we
could save some of this repeated work?
Reusability is the way of life in Python. `The Python Package Index (PyPI)
<https://pypi.org/>`_ has a vast range of packages you can use in your own
Python programs. Check out `Django Packages <https://djangopackages.org>`_ for
existing reusable apps you could incorporate in your project. Django itself is
also a normal Python package. This means that you can take existing Python
packages or Django apps and compose them into your own web project. You only
need to write the parts that make your project unique.
Let's say you were starting a new project that needed a polls app like the one
we've been working on. How do you make this app reusable? Luckily, you're well
on the way already. In :doc:`Tutorial 1 </intro/tutorial01>`, we saw how we
could decouple polls from the project-level URLconf using an ``include``.
In this tutorial, we'll take further steps to make the app easy to use in new
projects and ready to publish for others to install and use.
.. admonition:: Package? App?
A Python :term:`package` provides a way of grouping related Python code for
easy reuse. A package contains one or more files of Python code (also known
as "modules").
A package can be imported with ``import foo.bar`` or ``from foo import
bar``. For a directory (like ``polls``) to form a package, it must contain
a special file ``__init__.py``, even if this file is empty.
A Django *application* is a Python package that is specifically intended
for use in a Django project. An application may use common Django
conventions, such as having ``models``, ``tests``, ``urls``, and ``views``
submodules.
Later on we use the term *packaging* to describe the process of making a
Python package easy for others to install. It can be a little confusing, we
know.
Your project and your reusable app
==================================
After the previous tutorials, our project should look like this:
.. code-block:: text
mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py
asgi.py
wsgi.py
polls/
__init__.py
admin.py
apps.py
migrations/
__init__.py
0001_initial.py
models.py
static/
polls/
images/
background.png
style.css
templates/
polls/
detail.html
index.html
results.html
tests.py
urls.py
views.py
templates/
admin/
base_site.html
You created ``mysite/templates`` in :doc:`Tutorial 7 </intro/tutorial07>`,
and ``polls/templates`` in :doc:`Tutorial 3 </intro/tutorial03>`. Now perhaps
it is clearer why we chose to have separate template directories for the
project and application: everything that is part of the polls application is in
``polls``. It makes the application self-contained and easier to drop into a
new project.
The ``polls`` directory could now be copied into a new Django project and
immediately reused. It's not quite ready to be published though. For that, we
need to package the app to make it easy for others to install.
.. _installing-reusable-apps-prerequisites:
Installing some prerequisites
=============================
The current state of Python packaging is a bit muddled with various tools. For
this tutorial, we're going to use :pypi:`setuptools` to build our package. It's
the recommended packaging tool (merged with the ``distribute`` fork). We'll
also be using :pypi:`pip` to install and uninstall it. You should install these
two packages now. If you need help, you can refer to :ref:`how to install
Django with pip<installing-official-release>`. You can install ``setuptools``
the same way.
Packaging your app
==================
Python *packaging* refers to preparing your app in a specific format that can
be easily installed and used. Django itself is packaged very much like
this. For a small app like polls, this process isn't too difficult.
#. First, create a parent directory for the package, outside of your Django
project. Call this directory ``django-polls``.
.. admonition:: Choosing a name for your app
When choosing a name for your package, check PyPI to avoid naming
conflicts with existing packages. We recommend using a ``django-``
prefix for package names, to identify your package as specific to
Django, and a corresponding ``django_`` prefix for your module name. For
example, the ``django-ratelimit`` package contains the
``django_ratelimit`` module.
Application labels (that is, the final part of the dotted path to
application packages) *must* be unique in :setting:`INSTALLED_APPS`.
Avoid using the same label as any of the Django :doc:`contrib packages
</ref/contrib/index>`, for example ``auth``, ``admin``, or
``messages``.
#. Move the ``polls`` directory into ``django-polls`` directory, and rename it
to ``django_polls``.
#. Edit ``django_polls/apps.py`` so that :attr:`~.AppConfig.name` refers to the
new module name and add :attr:`~.AppConfig.label` to give a short name for
the app:
.. code-block:: python
:caption: ``django-polls/django_polls/apps.py``
from django.apps import AppConfig
class PollsConfig(AppConfig):
default_auto_field = "django.db.models.BigAutoField"
name = "django_polls"
label = "polls"
#. Create a file ``django-polls/README.rst`` with the following contents:
.. code-block:: rst
:caption: ``django-polls/README.rst``
============
django-polls
============
django-polls is a Django app to conduct web-based polls. For each
question, visitors can choose between a fixed number of answers.
Detailed documentation is in the "docs" directory.
Quick start
-----------
1. Add "polls" to your INSTALLED_APPS setting like this::
INSTALLED_APPS = [
...,
"django_polls",
]
2. Include the polls URLconf in your project urls.py like this::
path("polls/", include("django_polls.urls")),
3. Run ``python manage.py migrate`` to create the models.
4. Start the development server and visit the admin to create a poll.
5. Visit the ``/polls/`` URL to participate in the poll.
#. Create a ``django-polls/LICENSE`` file. Choosing a license is beyond the
scope of this tutorial, but suffice it to say that code released publicly
without a license is *useless*. Django and many Django-compatible apps are
distributed under the BSD license; however, you're free to pick your own
license. Just be aware that your licensing choice will affect who is able
to use your code.
#. Next we'll create the ``pyproject.toml`` file which details how to build and
install the app. A full explanation of this file is beyond the scope of this
tutorial, but the `Python Packaging User Guide
<https://packaging.python.org/guides/writing-pyproject-toml/>`_ has a good
explanation. Create the ``django-polls/pyproject.toml`` file with the
following contents:
.. code-block:: toml
:caption: ``django-polls/pyproject.toml``
[build-system]
requires = ["setuptools>=61.0"]
build-backend = "setuptools.build_meta"
[project]
name = "django-polls"
version = "0.1"
dependencies = [
"django>=X.Y", # Replace "X.Y" as appropriate
]
description = "A Django app to conduct web-based polls."
readme = "README.rst"
requires-python = ">= 3.10"
authors = [
{name = "Your Name", email = "yourname@example.com"},
]
classifiers = [
"Environment :: Web Environment",
"Framework :: Django",
"Framework :: Django :: X.Y", # Replace "X.Y" as appropriate
"Intended Audience :: Developers",
"License :: OSI Approved :: BSD License",
"Operating System :: OS Independent",
"Programming Language :: Python",
"Programming Language :: Python :: 3",
"Programming Language :: Python :: 3 :: Only",
"Programming Language :: Python :: 3.10",
"Programming Language :: Python :: 3.11",
"Programming Language :: Python :: 3.12",
"Topic :: Internet :: WWW/HTTP",
"Topic :: Internet :: WWW/HTTP :: Dynamic Content",
]
[project.urls]
Homepage = "https://www.example.com/"
#. Many common files and Python modules and packages are included in the
package by default. To include additional files, we'll need to create a
``MANIFEST.in`` file. To include the templates and static files, create a
file ``django-polls/MANIFEST.in`` with the following contents:
.. code-block:: text
:caption: ``django-polls/MANIFEST.in``
recursive-include django_polls/static *
recursive-include django_polls/templates *
#. It's optional, but recommended, to include detailed documentation with your
app. Create an empty directory ``django-polls/docs`` for future
documentation.
Note that the ``docs`` directory won't be included in your package unless
you add some files to it. Many Django apps also provide their documentation
online through sites like `readthedocs.org <https://readthedocs.org>`_.
#. Check that the :pypi:`build` package is installed (``python -m pip install
build``) and try building your package by running ``python -m build`` inside
``django-polls``. This creates a directory called ``dist`` and builds your
new package into source and binary formats, ``django-polls-0.1.tar.gz`` and
``django_polls-0.1-py3-none-any.whl``.
For more information on packaging, see Python's `Tutorial on Packaging and
Distributing Projects
<https://packaging.python.org/tutorials/packaging-projects/>`_.
Using your own package
======================
Since we moved the ``polls`` directory out of the project, it's no longer
working. We'll now fix this by installing our new ``django-polls`` package.
.. admonition:: Installing as a user library
The following steps install ``django-polls`` as a user library. Per-user
installs have a lot of advantages over installing the package system-wide,
such as being usable on systems where you don't have administrator access
as well as preventing the package from affecting system services and other
users of the machine.
Note that per-user installations can still affect the behavior of system
tools that run as that user, so using a virtual environment is a more robust
solution (see below).
#. To install the package, use pip (you already :ref:`installed it
<installing-reusable-apps-prerequisites>`, right?):
.. code-block:: shell
python -m pip install --user django-polls/dist/django-polls-0.1.tar.gz
#. Update ``mysite/settings.py`` to point to the new module name::
INSTALLED_APPS = [
"django_polls.apps.PollsConfig",
...,
]
#. Update ``mysite/urls.py`` to point to the new module name::
urlpatterns = [
path("polls/", include("django_polls.urls")),
...,
]
#. Run the development server to confirm the project continues to work.
Publishing your app
===================
Now that we've packaged and tested ``django-polls``, it's ready to share with
the world! If this wasn't just an example, you could now:
* Email the package to a friend.
* Upload the package on your website.
* Post the package on a public repository, such as `the Python Package Index
(PyPI)`_. `packaging.python.org <https://packaging.python.org>`_ has `a good
tutorial <https://packaging.python.org/tutorials/packaging-projects/#uploading-the-distribution-archives>`_
for doing this.
Installing Python packages with a virtual environment
=====================================================
Earlier, we installed ``django-polls`` as a user library. This has some
disadvantages:
* Modifying the user libraries can affect other Python software on your system.
* You won't be able to run multiple versions of this package (or others with
the same name).
Typically, these situations only arise once you're maintaining several Django
projects. When they do, the best solution is to use :doc:`venv
<python:tutorial/venv>`. This tool allows you to maintain multiple isolated
Python environments, each with its own copy of the libraries and package
namespace.