Fixed #16671 - Added a tutorial on reuseable apps

Thank-you Katie Miller and Ben Sturmfels for the initial draft,
as well as Russ and Carl for the reviews.
This commit is contained in:
Tim Graham 2012-10-30 15:53:56 -04:00
parent 2f035a9723
commit 08cf54990a
6 changed files with 388 additions and 8 deletions

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@ -380,6 +380,7 @@ answer newbie questions, and generally made Django that much better:
Christian Metts Christian Metts
michal@plovarna.cz michal@plovarna.cz
Slawek Mikula <slawek dot mikula at gmail dot com> Slawek Mikula <slawek dot mikula at gmail dot com>
Katie Miller <katie@sub50.com>
Shawn Milochik <shawn@milochik.com> Shawn Milochik <shawn@milochik.com>
mitakummaa@gmail.com mitakummaa@gmail.com
Taylor Mitchell <taylor.mitchell@gmail.com> Taylor Mitchell <taylor.mitchell@gmail.com>
@ -510,6 +511,7 @@ answer newbie questions, and generally made Django that much better:
Johan C. Stöver <johan@nilling.nl> Johan C. Stöver <johan@nilling.nl>
Nowell Strite <http://nowell.strite.org/> Nowell Strite <http://nowell.strite.org/>
Thomas Stromberg <tstromberg@google.com> Thomas Stromberg <tstromberg@google.com>
Ben Sturmfels <ben@sturm.com.au>
Travis Swicegood <travis@domain51.com> Travis Swicegood <travis@domain51.com>
Pascal Varet Pascal Varet
SuperJared SuperJared

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@ -46,6 +46,9 @@ Are you new to Django or to programming? This is the place to start!
:doc:`Part 3 <intro/tutorial03>` | :doc:`Part 3 <intro/tutorial03>` |
:doc:`Part 4 <intro/tutorial04>` :doc:`Part 4 <intro/tutorial04>`
* **Advanced Tutorials:**
:doc:`How to write reusable apps <intro/reusable-apps>`
The model layer The model layer
=============== ===============

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@ -6,31 +6,32 @@ place: read this material to quickly get up and running.
.. toctree:: .. toctree::
:maxdepth: 1 :maxdepth: 1
overview overview
install install
tutorial01 tutorial01
tutorial02 tutorial02
tutorial03 tutorial03
tutorial04 tutorial04
reusable-apps
whatsnext whatsnext
.. seealso:: .. seealso::
If you're new to Python_, you might want to start by getting an idea of what If you're new to Python_, you might want to start by getting an idea of what
the language is like. Django is 100% Python, so if you've got minimal the language is like. Django is 100% Python, so if you've got minimal
comfort with Python you'll probably get a lot more out of Django. comfort with Python you'll probably get a lot more out of Django.
If you're new to programming entirely, you might want to start with this If you're new to programming entirely, you might want to start with this
`list of Python resources for non-programmers`_ `list of Python resources for non-programmers`_
If you already know a few other languages and want to get up to speed with If you already know a few other languages and want to get up to speed with
Python quickly, we recommend `Dive Into Python`_ (also available in a Python quickly, we recommend `Dive Into Python`_ (also available in a
`dead-tree version`_). If that's not quite your style, there are quite `dead-tree version`_). If that's not quite your style, there are quite
a few other `books about Python`_. a few other `books about Python`_.
.. _python: http://python.org/ .. _python: http://python.org/
.. _list of Python resources for non-programmers: http://wiki.python.org/moin/BeginnersGuide/NonProgrammers .. _list of Python resources for non-programmers: http://wiki.python.org/moin/BeginnersGuide/NonProgrammers
.. _dive into python: http://diveintopython.net/ .. _dive into python: http://diveintopython.net/
.. _dead-tree version: http://www.amazon.com/exec/obidos/ASIN/1590593561/ref=nosim/jacobian20 .. _dead-tree version: http://www.amazon.com/exec/obidos/ASIN/1590593561/ref=nosim/jacobian20
.. _books about Python: http://wiki.python.org/moin/PythonBooks .. _books about Python: http://wiki.python.org/moin/PythonBooks

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@ -0,0 +1,363 @@
=============================================
Advanced tutorial: How to write reusable apps
=============================================
This advanced tutorial begins where :doc:`Tutorial 4 </intro/tutorial04>` 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 14, 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)
<http://guide.python-distribute.org/contributing.html#pypi-info>`_ has a vast
range of packages you can use in your own Python programs. Check out `Django
Packages <http://www.djangopackages.com>`_ for existing reusable apps you could
incorporate in your project. Django itself is also just a 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 3 </intro/tutorial03>`, 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 `package <http://docs.python.org/tutorial/modules.html#packages>`_
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 *app* is just a Python package that is specifically intended for
use in a Django project. An app may also use common Django conventions,
such as having a ``models.py`` file.
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.
Completing your reusable app
============================
After the previous tutorials, our project should look like this::
mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py
wsgi.py
polls/
admin.py
__init__.py
models.py
tests.py
urls.py
views.py
You also have a directory somewhere called ``mytemplates`` which you created in
:doc:`Tutorial 2 </intro/tutorial02>`. You specified its location in the
TEMPLATE_DIRS setting. This directory should look like this::
mytemplates/
admin/
base_site.html
polls/
detail.html
index.html
results.html
The polls app is already a Python package, thanks to the ``polls/__init__.py``
file. That's a great start, but we can't just pick up this package and drop it
into a new project. The polls templates are currently stored in the
project-wide ``mytemplates`` directory. To make the app self-contained, it
should also contain the necessary templates.
Inside the ``polls`` app, create a new ``templates`` directory. Now move the
``polls`` template directory from ``mytemplates`` into the new
``templates``. Your project should now look like this::
mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py
wsgi.py
polls/
admin.py
__init__.py
models.py
templates/
polls/
detail.html
index.html
results.html
tests.py
urls.py
views.py
Your project-wide templates directory should now look like this::
mytemplates/
admin/
base_site.html
Looking good! Now would be a good time to confirm that your polls application
still works correctly. How does Django know how to find the new location of
the polls templates even though we didn't modify :setting:`TEMPLATE_DIRS`?
Django has a :setting:`TEMPLATE_LOADERS` setting which contains a list
of callables that know how to import templates from various sources. One of
the defaults is :class:`django.template.loaders.app_directories.Loader` which
looks for a "templates" subdirectory in each of the :setting:`INSTALLED_APPS`.
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.
.. admonition:: Why nested?
Why create a ``polls`` directory under ``templates`` when we're
already inside the polls app? This directory is needed to avoid conflicts in
Django's ``app_directories`` template loader. For example, if two
apps had a template called ``base.html``, without the extra directory it
wouldn't be possible to distinguish between the two. It's a good convention
to use the name of your app for this directory.
.. _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 distribute_ to build our package. It's a
community-maintained fork of the older ``setuptools`` project. We'll also be
using `pip`_ to uninstall it after we're finished. 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 ``distribute``
the same way.
.. _distribute: http://pypi.python.org/pypi/distribute
.. _pip: http://pypi.python.org/pypi/pip
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.
1. First, create a parent directory for ``polls``, 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 resources like PyPI to avoid
naming conflicts with existing packages. It's often useful to prepend
``django-`` to your module name when creating a package to distribute.
This helps others looking for Django apps identify your app as Django
specific.
2. Move the ``polls`` directory into the ``django-polls`` directory.
3. Create a file ``django-polls/README.txt`` with the following contents::
=====
Polls
=====
Polls is a simple 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 = (
...
'polls',
)
2. Include the polls URLconf in your project urls.py like this::
url(r'^polls/', include('polls.urls')),
3. Run `python manage.py syncdb` to create the polls models.
4. Start the development server and visit http://127.0.0.1:8000/admin/
to create a poll (you'll need the Admin app enabled).
5. Visit http://127.0.0.1:8000/polls/ to participate in the poll.
4. 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.
5. Next we'll create a ``setup.py`` file which provides details about how to
build and install the app. A full explanation of this file is beyond the
scope of this tutorial, but the `distribute docs
<http://packages.python.org/distribute/setuptools.html>`_ have a good explanation.
Create a file ``django-polls/setup.py`` with the following contents::
import os
from setuptools import setup
README = open(os.path.join(os.path.dirname(__file__), 'README.txt')).read()
# allow setup.py to be run from any path
os.chdir(os.path.normpath(os.path.join(os.path.abspath(__file__), os.pardir)))
setup(
name = 'django-polls',
version = '0.1',
packages = ['polls'],
include_package_data = True,
license = 'BSD License', # example license
description = 'A simple Django app to conduct Web-based polls.',
long_description = README,
url = 'http://www.example.com/',
author = 'Your Name',
author_email = 'yourname@example.com',
classifiers = [
'Environment :: Web Environment',
'Framework :: Django',
'Intended Audience :: Developers',
'License :: OSI Approved :: BSD License', # example license
'Operating System :: OS Independent',
'Programming Language :: Python',
'Programming Language :: Python :: 2.6',
'Programming Language :: Python :: 2.7',
'Topic :: Internet :: WWW/HTTP',
'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
],
)
.. admonition:: I thought you said we were going to use ``distribute``?
Distribute is a drop-in replacement for ``setuptools``. Even though we
appear to import from ``setuptools``, since we have ``distribute``
installed, it will override the import.
6. Only Python modules and packages are included in the package by default. To
include additional files, we'll need to create a ``MANIFEST.in`` file. The
distribute docs referred to in the previous step discuss this file in more
details. To include the templates and our LICENSE file, create a file
``django-polls/MANIFEST.in`` with the following contents::
include LICENSE
recursive-include polls/templates *
7. It's optional, but recommended, to include detailed documentation with your
app. Create an empty directory ``django-polls/docs`` for future
documentation. Add an additional line to ``django-polls/MANIFEST.in``::
recursive-include docs *
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 <http://readthedocs.org>`_.
8. Try building your package with ``python setup.py sdist`` (run from inside
``django-polls``). This creates a directory called ``dist`` and builds your
new package, ``django-polls-0.1.tar.gz``.
For more information on packaging, see `The Hitchhiker's Guide to Packaging
<http://guide.python-distribute.org/quickstart.html>`_.
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 system library
The following steps install ``django-polls`` as a system library. In
general, it's best to avoid messing with your system libraries to avoid
breaking things. For this simple example though, the risk is low and it will
help with understanding packaging. We'll explain how to uninstall in
step 4.
For experienced users, a neater way to manage your packages is to use
"virtualenv" (see below).
1. Inside ``django-polls/dist``, untar the new package
``django-polls-0.1.tar.gz`` (e.g. ``tar xzvf django-polls-0.1.tar.gz``). If
you're using Windows, you can download the command-line tool bsdtar_ to do
this, or you can use a GUI-based tool such as 7-zip_.
2. Change into the directory created in step 1 (e.g. ``cd django-polls-0.1``).
3. If you're using GNU/Linux, Mac OS X or some other flavor of Unix, enter the
command ``sudo python setup.py install`` at the shell prompt. If you're
using Windows, start up a command shell with administrator privileges and
run the command ``setup.py install``.
With luck, your Django project should now work correctly again. Run the
server again to confirm this.
4. To uninstall the package, use pip (you already :ref:`installed it
<installing-reusable-apps-prerequisites>`, right?)::
sudo pip uninstall django-polls
.. _bsdtar: http://gnuwin32.sourceforge.net/packages/bsdtar.htm
.. _7-zip: http://www.7-zip.org/
.. _pip: http://pypi.python.org/pypi/pip
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 Web site.
* Post the package on a public repository, such as `The Python Package Index
(PyPI) <http://guide.python-distribute.org/contributing.html#pypi-info>`_.
For more information on PyPI, see the `Quickstart
<http://guide.python-distribute.org/quickstart.html#register-your-package-with-the-python-package-index-pypi>`_
section of The Hitchhiker's Guide to Packaging. One detail this guide mentions
is choosing the license under which your code is distributed.
Installing Python packages with virtualenv
==========================================
Earlier, we installed the polls app as a system library. This has some
disadvantages:
* Modifying the system 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 `virtualenv
<http://www.virtualenv.org/>`_. This tool allows you to maintain multiple
isolated Python environments, each with its own copy of the libraries and
package namespace.

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@ -315,6 +315,12 @@ Load the page in your Web browser, and you should see a bulleted-list
containing the "What's up" poll from Tutorial 1. The link points to the poll's containing the "What's up" poll from Tutorial 1. The link points to the poll's
detail page. detail page.
.. admonition:: Organizing Templates
Rather than one big templates directory, you can also store templates
within each app. We'll discuss this in more detail in the :doc:`reusable
apps tutorial</intro/reusable-apps>`.
A shortcut: :func:`~django.shortcuts.render` A shortcut: :func:`~django.shortcuts.render`
-------------------------------------------- --------------------------------------------

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@ -278,5 +278,10 @@ For full details on generic views, see the :doc:`generic views documentation
What's next? What's next?
============ ============
The tutorial ends here for the time being. In the meantime, you might want to The beginner tutorial ends here for the time being. In the meantime, you might
check out some pointers on :doc:`where to go from here </intro/whatsnext>`. want to check out some pointers on :doc:`where to go from here
</intro/whatsnext>`.
If you are familiar with Python packaging and interested in learning how to
turn polls into a "reusable app", check out :doc:`Advanced tutorial: How to
write reusable apps</intro/reusable-apps>`.