===================================
Writing your first patch for Django
===================================

Introduction
============

Interested in giving back to the community a little? Maybe you've found a bug
in Django that you'd like to see fixed, or maybe there's a small feature you
want added.

Contributing back to Django itself is the best way to see your own concerns
addressed. This may seem daunting at first, but it's really pretty simple.
We'll walk you through the entire process, so you can learn by example.

Who's this tutorial for?
------------------------

.. seealso::

    If you are looking for a reference on how to submit patches, see the
    :doc:`/internals/contributing/writing-code/submitting-patches`
    documentation.

For this tutorial, we expect that you have at least a basic understanding of
how Django works. This means you should be comfortable going through the
existing tutorials on :doc:`writing your first Django app</intro/tutorial01>`.
In addition, you should have a good understanding of Python itself. But if you
don't, `Dive Into Python`__ is a fantastic (and free) online book for
beginning Python programmers.

Those of you who are unfamiliar with version control systems and Trac will find
that this tutorial and its links include just enough information to get started.
However, you'll probably want to read some more about these different tools if
you plan on contributing to Django regularly.

For the most part though, this tutorial tries to explain as much as possible,
so that it can be of use to the widest audience.

.. admonition:: Where to get help:

    If you're having trouble going through this tutorial, please post a message
    to |django-developers| or drop by `#django-dev on irc.freenode.net`__ to
    chat with other Django users who might be able to help.

__ https://diveinto.org/python3/table-of-contents.html
__ irc://irc.freenode.net/django-dev

What does this tutorial cover?
------------------------------

We'll be walking you through contributing a patch to Django for the first time.
By the end of this tutorial, you should have a basic understanding of both the
tools and the processes involved. Specifically, we'll be covering the following:

* Installing Git.
* Downloading a copy of Django's development version.
* Running Django's test suite.
* Writing a test for your patch.
* Writing the code for your patch.
* Testing your patch.
* Submitting a pull request.
* Where to look for more information.

Once you're done with the tutorial, you can look through the rest of
:doc:`Django's documentation on contributing</internals/contributing/index>`.
It contains lots of great information and is a must read for anyone who'd like
to become a regular contributor to Django. If you've got questions, it's
probably got the answers.

.. admonition:: Python 3 required!

    The current version of Django doesn't support Python 2.7. Get Python 3 at
    `Python's download page <https://www.python.org/downloads/>`_ or with your
    operating system's package manager.

.. admonition:: For Windows users

    When installing Python on Windows, make sure you check the option "Add
    python.exe to Path", so that it is always available on the command line.

Code of Conduct
===============

As a contributor, you can help us keep the Django community open and inclusive.
Please read and follow our `Code of Conduct <https://www.djangoproject.com/conduct/>`_.

Installing Git
==============

For this tutorial, you'll need Git installed to download the current
development version of Django and to generate patch files for the changes you
make.

To check whether or not you have Git installed, enter ``git`` into the command
line. If you get messages saying that this command could not be found, you'll
have to download and install it, see `Git's download page`__.

If you're not that familiar with Git, you can always find out more about its
commands (once it's installed) by typing ``git help`` into the command line.

__ https://git-scm.com/download

Getting a copy of Django's development version
==============================================

The first step to contributing to Django is to get a copy of the source code.
First, `fork Django on GitHub <https://github.com/django/django/fork>`__. Then,
from the command line, use the ``cd`` command to navigate to the directory
where you'll want your local copy of Django to live.

Download the Django source code repository using the following command:

.. console::

    $ git clone https://github.com/YourGitHubName/django.git

.. admonition:: Low bandwidth connection?

    You can add the ``--depth 1`` argument to ``git clone`` to skip downloading
    all of Django's commit history, which reduces data transfer from  ~250 MB
    to ~70 MB.

Now that you have a local copy of Django, you can install it just like you would
install any package using ``pip``. The most convenient way to do so is by using
a *virtual environment*, which is a feature built into Python that allows you
to keep a separate directory of installed packages for each of your projects so
that they don't interfere with each other.

It's a good idea to keep all your virtual environments in one place, for
example in ``.virtualenvs/`` in your home directory.

Create a new virtual environment by running:

.. console::

    $ python3 -m venv ~/.virtualenvs/djangodev

The path is where the new environment will be saved on your computer.

The final step in setting up your virtual environment is to activate it:

.. code-block:: console

    $ source ~/.virtualenvs/djangodev/bin/activate

If the ``source`` command is not available, you can try using a dot instead:

.. code-block:: console

    $ . ~/.virtualenvs/djangodev/bin/activate

.. admonition:: For Windows users

    To activate your virtual environment on Windows, run:

    .. code-block:: doscon

        ...\> %HOMEPATH%\.virtualenvs\djangodev\Scripts\activate.bat

You have to activate the virtual environment whenever you open a new
terminal window. virtualenvwrapper__ is a useful tool for making this
more convenient.

__ https://virtualenvwrapper.readthedocs.io/en/latest/

The name of the currently activated virtual environment is displayed on the
command line to help you keep track of which one you are using. Anything you
install through ``pip`` while this name is displayed will be installed in that
virtual environment, isolated from other environments and system-wide packages.

.. _intro-contributing-install-local-copy:

Go ahead and install the previously cloned copy of Django:

.. console::

    $ pip install -e /path/to/your/local/clone/django/

The installed version of Django is now pointing at your local copy by installing
in editable mode. You will immediately see any changes you make to it, which is
of great help when writing your first patch.

Creating projects with a local copy of Django
---------------------------------------------

It may be helpful to test your local changes with a Django project. First you
have to create a new virtual environment, :ref:`install the previously cloned
local copy of Django in editable mode <intro-contributing-install-local-copy>`,
and create a new Django project outside of your local copy of Django. You will
immediately see any changes you make to Django in your new project, which is
of great help when writing your first patch.

Running Django's test suite for the first time
==============================================

When contributing to Django it's very important that your code changes don't
introduce bugs into other areas of Django. One way to check that Django still
works after you make your changes is by running Django's test suite. If all
the tests still pass, then you can be reasonably sure that your changes
work and haven't broken other parts Django. If you've never run Django's test
suite before, it's a good idea to run it once beforehand to get familiar with
its output.

Before running the test suite, install its dependencies by ``cd``-ing into the
Django ``tests/`` directory and then running:

.. console::

    $ pip install -r requirements/py3.txt

If you encounter an error during the installation, your system might be missing
a dependency for one or more of the Python packages. Consult the failing
package's documentation or search the Web with the error message that you
encounter.

Now we are ready to run the test suite. If you're using GNU/Linux, macOS, or
some other flavor of Unix, run:

.. console::

    $ ./runtests.py

Now sit back and relax. Django's entire test suite has thousands of tests, and
it takes at least a few minutes run, depending on the speed of your computer.

While Django's test suite is running, you'll see a stream of characters
representing the status of each test as it completes. ``E`` indicates that an
error was raised during a test, and ``F`` indicates that a test's assertions
failed. Both of these are considered to be test failures. Meanwhile, ``x`` and
``s`` indicated expected failures and skipped tests, respectively. Dots indicate
passing tests.

Skipped tests are typically due to missing external libraries required to run
the test; see :ref:`running-unit-tests-dependencies` for a list of dependencies
and be sure to install any for tests related to the changes you are making (we
won't need any for this tutorial). Some tests are specific to a particular
database backend and will be skipped if not testing with that backend. SQLite
is the database backend for the default settings. To run the tests using a
different backend, see :ref:`running-unit-tests-settings`.

Once the tests complete, you should be greeted with a message informing you
whether the test suite passed or failed. Since you haven't yet made any changes
to Django's code, the entire test suite **should** pass. If you get failures or
errors make sure you've followed all of the previous steps properly. See
:ref:`running-unit-tests` for more information.

Note that the latest Django master may not always be stable. When developing
against master, you can check `Django's continuous integration builds`__ to
determine if the failures are specific to your machine or if they are also
present in Django's official builds. If you click to view a particular build,
you can view the "Configuration Matrix" which shows failures broken down by
Python version and database backend.

__ https://djangoci.com

.. note::

    For this tutorial and the ticket we're working on, testing against SQLite
    is sufficient, however, it's possible (and sometimes necessary) to
    :ref:`run the tests using a different database
    <running-unit-tests-settings>`.

Working on a feature
====================

For this tutorial, we'll work on a "fake ticket" as a case study. Here are the
imaginary details:

.. admonition:: Ticket #99999 -- Allow making toast

    Django should provide a function ``django.shortcuts.make_toast()`` that
    returns ``'toast'``.

We'll now implement this feature and associated tests.

Creating a branch for your patch
================================

Before making any changes, create a new branch for the ticket:

.. console::

    $ git checkout -b ticket_99999

You can choose any name that you want for the branch, "ticket_99999" is an
example. All changes made in this branch will be specific to the ticket and
won't affect the main copy of the code that we cloned earlier.

Writing some tests for your ticket
==================================

In most cases, for a patch to be accepted into Django it has to include tests.
For bug fix patches, this means writing a regression test to ensure that the
bug is never reintroduced into Django later on. A regression test should be
written in such a way that it will fail while the bug still exists and pass
once the bug has been fixed. For patches containing new features, you'll need
to include tests which ensure that the new features are working correctly.
They too should fail when the new feature is not present, and then pass once it
has been implemented.

A good way to do this is to write your new tests first, before making any
changes to the code. This style of development is called
`test-driven development`__ and can be applied to both entire projects and
single patches. After writing your tests, you then run them to make sure that
they do indeed fail (since you haven't fixed that bug or added that feature
yet). If your new tests don't fail, you'll need to fix them so that they do.
After all, a regression test that passes regardless of whether a bug is present
is not very helpful at preventing that bug from reoccurring down the road.

Now for our hands-on example.

__ https://en.wikipedia.org/wiki/Test-driven_development

Writing a test for ticket #99999
--------------------------------

In order to resolve this ticket, we'll add a ``make_toast()`` function to the
top-level ``django`` module. First we are going to write a test that tries to
use the function and check that its output looks correct.

Navigate to Django's ``tests/shortcuts/`` folder and create a new file
``test_make_toast.py``. Add the following code::

    from django.shortcuts import make_toast
    from django.test import SimpleTestCase


    class MakeToastTests(SimpleTestCase):
        def test_make_toast(self):
            self.assertEqual(make_toast(), 'toast')

This test checks that the ``make_toast()`` returns ``'toast'``.

.. admonition:: But this testing thing looks kinda hard...

    If you've never had to deal with tests before, they can look a little hard
    to write at first glance. Fortunately, testing is a *very* big subject in
    computer programming, so there's lots of information out there:

    * A good first look at writing tests for Django can be found in the
      documentation on :doc:`/topics/testing/overview`.
    * Dive Into Python (a free online book for beginning Python developers)
      includes a great `introduction to Unit Testing`__.
    * After reading those, if you want something a little meatier to sink
      your teeth into, there's always the Python :mod:`unittest` documentation.

__ https://www.diveinto.org/python3/unit-testing.html

Running your new test
---------------------

Since we haven't made any modifications to ``django.shortcuts`` yet, our test
should fail. Let's run all the tests in the ``shortcuts`` folder to make sure
that's really what happens. ``cd`` to the Django ``tests/`` directory and run:

.. console::

    $ ./runtests.py shortcuts

If the tests ran correctly, you should see one failure corresponding to the test
method we added, with this error::

    ImportError: cannot import name 'make_toast' from 'django.shortcuts'

If all of the tests passed, then you'll want to make sure that you added the
new test shown above to the appropriate folder and file name.

Writing the code for your ticket
================================

Next we'll be adding the ``make_toast()`` function.

Navigate to the ``django/`` folder and open the ``shortcuts.py`` file. At the
bottom, add::

    def make_toast():
        return 'toast'

Now we need to make sure that the test we wrote earlier passes, so we can see
whether the code we added is working correctly. Again, navigate to the Django
``tests/`` directory and run:

.. console::

    $ ./runtests.py shortcuts

Everything should pass. If it doesn't, make sure you correctly added the
function to the correct file.

Running Django's test suite for the second time
===============================================

Once you've verified that your patch and your test are working correctly, it's
a good idea to run the entire Django test suite just to verify that your change
hasn't introduced any bugs into other areas of Django. While successfully
passing the entire test suite doesn't guarantee your code is bug free, it does
help identify many bugs and regressions that might otherwise go unnoticed.

To run the entire Django test suite, ``cd`` into the Django ``tests/``
directory and run:

.. console::

    $ ./runtests.py

Writing Documentation
=====================

This is a new feature, so it should be documented. Open the file
``docs/topics/http/shortcuts.txt`` and add the following at the end of the
file::

    ``make_toast()``
    ================

    .. versionadded:: 2.2

    Returns ``'toast'``.

Since this new feature will be in an upcoming release it is also added to the
release notes for the next version of Django. Open the release notes for the
latest version in ``docs/releases/``, which at time of writing is ``2.2.txt``.
Add a note under the "Minor Features" header::

    :mod:`django.shortcuts`
    ~~~~~~~~~~~~~~~~~~~~~~~

    * The new :func:`django.shortcuts.make_toast` function returns ``'toast'``.

For more information on writing documentation, including an explanation of what
the ``versionadded`` bit is all about, see
:doc:`/internals/contributing/writing-documentation`. That page also includes
an explanation of how to build a copy of the documentation locally, so you can
preview the HTML that will be generated.

Previewing your changes
=======================

Now it's time to go through all the changes made in our patch. To stage all the
changes ready for commit, run:

.. console::

    $ git add --all

Then display the differences between your current copy of Django (with your
changes) and the revision that you initially checked out earlier in the
tutorial with:

.. console::

    $ git diff --cached

Use the arrow keys to move up and down.

.. code-block:: diff

    diff --git a/django/shortcuts.py b/django/shortcuts.py
    index 7ab1df0e9d..8dde9e28d9 100644
    --- a/django/shortcuts.py
    +++ b/django/shortcuts.py
    @@ -156,3 +156,7 @@ def resolve_url(to, *args, **kwargs):

         # Finally, fall back and assume it's a URL
         return to
    +
    +
    +def make_toast():
    +    return 'toast'
    diff --git a/docs/releases/2.2.txt b/docs/releases/2.2.txt
    index 7d85d30c4a..81518187b3 100644
    --- a/docs/releases/2.2.txt
    +++ b/docs/releases/2.2.txt
    @@ -40,6 +40,11 @@ database constraints. Constraints are added to models using the
     Minor features
     --------------

    +:mod:`django.shortcuts`
    +~~~~~~~~~~~~~~~~~~~~~~~
    +
    +* The new :func:`django.shortcuts.make_toast` function returns ``'toast'``.
    +
     :mod:`django.contrib.admin`
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~

    diff --git a/docs/topics/http/shortcuts.txt b/docs/topics/http/shortcuts.txt
    index 7b3a3a2c00..711bf6bb6d 100644
    --- a/docs/topics/http/shortcuts.txt
    +++ b/docs/topics/http/shortcuts.txt
    @@ -271,3 +271,12 @@ This example is equivalent to::
             my_objects = list(MyModel.objects.filter(published=True))
             if not my_objects:
                 raise Http404("No MyModel matches the given query.")
    +
    +``make_toast()``
    +================
    +
    +.. function:: make_toast()
    +
    +.. versionadded:: 2.2
    +
    +Returns ``'toast'``.
    diff --git a/tests/shortcuts/test_make_toast.py b/tests/shortcuts/test_make_toast.py
    new file mode 100644
    index 0000000000..6f4c627b6e
    --- /dev/null
    +++ b/tests/shortcuts/test_make_toast.py
    @@ -0,0 +1,7 @@
    +from django.shortcuts import make_toast
    +from django.test import SimpleTestCase
    +
    +
    +class MakeToastTests(SimpleTestCase):
    +    def test_make_toast(self):
    +        self.assertEqual(make_toast(), 'toast')

When you're done previewing the patch, hit the ``q`` key to return to the
command line. If the patch's content looked okay, it's time to commit the
changes.

Committing the changes in the patch
===================================

To commit the changes:

.. console::

    $ git commit

This opens up a text editor to type the commit message. Follow the :ref:`commit
message guidelines <committing-guidelines>` and write a message like:

.. code-block:: text

    Fixed #99999 -- Added a shortcut function to make toast.

Pushing the commit and making a pull request
============================================

After committing the patch, send it to your fork on GitHub (substitute
"ticket_99999" with the name of your branch if it's different):

.. console::

    $ git push origin ticket_99999

You can create a pull request by visiting the `Django GitHub page
<https://github.com/django/django/>`_. You'll see your branch under "Your
recently pushed branches". Click "Compare & pull request" next to it.

Please don't do it for this tutorial, but on the next page that displays a
preview of the patch, you would click "Create pull request".

Next steps
==========

Congratulations, you've learned how to make a pull request to Django! Details
of more advanced techniques you may need are in
:doc:`/internals/contributing/writing-code/working-with-git`.

Now you can put those skills to good use by helping to improve Django's
codebase.

More information for new contributors
-------------------------------------

Before you get too into writing patches for Django, there's a little more
information on contributing that you should probably take a look at:

* You should make sure to read Django's documentation on
  :doc:`claiming tickets and submitting patches
  </internals/contributing/writing-code/submitting-patches>`.
  It covers Trac etiquette, how to claim tickets for yourself, expected
  coding style for patches, and many other important details.
* First time contributors should also read Django's :doc:`documentation
  for first time contributors</internals/contributing/new-contributors/>`.
  It has lots of good advice for those of us who are new to helping out
  with Django.
* After those, if you're still hungry for more information about
  contributing, you can always browse through the rest of
  :doc:`Django's documentation on contributing</internals/contributing/index>`.
  It contains a ton of useful information and should be your first source
  for answering any questions you might have.

Finding your first real ticket
------------------------------

Once you've looked through some of that information, you'll be ready to go out
and find a ticket of your own to write a patch for. Pay special attention to
tickets with the "easy pickings" criterion. These tickets are often much
simpler in nature and are great for first time contributors. Once you're
familiar with contributing to Django, you can move on to writing patches for
more difficult and complicated tickets.

If you just want to get started already (and nobody would blame you!), try
taking a look at the list of `easy tickets that need patches`__ and the
`easy tickets that have patches which need improvement`__. If you're familiar
with writing tests, you can also look at the list of
`easy tickets that need tests`__. Just remember to follow the guidelines about
claiming tickets that were mentioned in the link to Django's documentation on
:doc:`claiming tickets and submitting patches
</internals/contributing/writing-code/submitting-patches>`.

__ https://code.djangoproject.com/query?status=new&status=reopened&has_patch=0&easy=1&col=id&col=summary&col=status&col=owner&col=type&col=milestone&order=priority
__ https://code.djangoproject.com/query?status=new&status=reopened&needs_better_patch=1&easy=1&col=id&col=summary&col=status&col=owner&col=type&col=milestone&order=priority
__ https://code.djangoproject.com/query?status=new&status=reopened&needs_tests=1&easy=1&col=id&col=summary&col=status&col=owner&col=type&col=milestone&order=priority

What's next after creating a pull request?
------------------------------------------

After a ticket has a patch, it needs to be reviewed by a second set of eyes.
After submitting a pull request, update the ticket metadata by setting the
flags on the ticket to say "has patch", "doesn't need tests", etc, so others
can find it for review. Contributing doesn't necessarily always mean writing a
patch from scratch. Reviewing existing patches is also a very helpful
contribution. See :doc:`/internals/contributing/triaging-tickets` for details.
