{"title":"Advanced tutorial: How to write reusable apps","version":"1.11","locale":"en","docname":"intro/reusable-apps","url":"/en/1.11/intro/reusable-apps/","canonical":"https://djangodocs.dev/en/1.11/intro/reusable-apps/","summary":"This advanced tutorial begins where Tutorial 7 left off. We’ll be turning our Web-poll into a standalone Python package you can reuse in new projects and share with…","html":"

Advanced tutorial: How to write reusable appsLink to this heading#

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This advanced tutorial begins where Tutorial 7\nleft off. We’ll be turning our Web-poll into a standalone Python package\nyou can reuse in new projects and share with other people.

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If you haven’t recently completed Tutorials 1–7, we encourage you to review\nthese so that your example project matches the one described below.

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Reusability mattersLink to this heading#

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It’s a lot of work to design, build, test and maintain a web application. Many\nPython and Django projects share common problems. Wouldn’t it be great if we\ncould save some of this repeated work?

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Reusability is the way of life in Python. The Python Package Index (PyPI) has a vast range of packages you can use in\nyour own Python programs. Check out Django Packages for existing reusable apps you could incorporate\nin your project. Django itself is also just a Python package. This means that\nyou can take existing Python packages or Django apps and compose them into your\nown web project. You only need to write the parts that make your project unique.

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Let’s say you were starting a new project that needed a polls app like the one\nwe’ve been working on. How do you make this app reusable? Luckily, you’re well\non the way already. In Tutorial 3, we saw how we\ncould decouple polls from the project-level URLconf using an include.\nIn this tutorial, we’ll take further steps to make the app easy to use in new\nprojects and ready to publish for others to install and use.

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Your project and your reusable appLink to this heading#

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After the previous tutorials, our project should look like this:

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Code
mysite/\n    manage.py\n    mysite/\n        __init__.py\n        settings.py\n        urls.py\n        wsgi.py\n    polls/\n        __init__.py\n        admin.py\n        migrations/\n            __init__.py\n            0001_initial.py\n        models.py\n        static/\n            polls/\n                images/\n                    background.gif\n                style.css\n        templates/\n            polls/\n                detail.html\n                index.html\n                results.html\n        tests.py\n        urls.py\n        views.py\n    templates/\n        admin/\n            base_site.html\n
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You created mysite/templates in Tutorial 7,\nand polls/templates in Tutorial 3. Now perhaps\nit is clearer why we chose to have separate template directories for the\nproject and application: everything that is part of the polls application is in\npolls. It makes the application self-contained and easier to drop into a\nnew project.

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The polls directory could now be copied into a new Django project and\nimmediately reused. It’s not quite ready to be published though. For that, we\nneed to package the app to make it easy for others to install.

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Installing some prerequisitesLink to this heading#

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The current state of Python packaging is a bit muddled with various tools. For\nthis tutorial, we’re going to use setuptools to build our package. It’s the\nrecommended packaging tool (merged with the distribute fork). We’ll also be\nusing pip to install and uninstall it. You should install these\ntwo packages now. If you need help, you can refer to how to install\nDjango with pip. You can install setuptools\nthe same way.

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Packaging your appLink to this heading#

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Python packaging refers to preparing your app in a specific format that can\nbe easily installed and used. Django itself is packaged very much like\nthis. For a small app like polls, this process isn’t too difficult.

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  1. First, create a parent directory for polls, outside of your Django\nproject. Call this directory django-polls.

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    2. \n

  2. Move the polls directory into the django-polls directory.

    3. \n

  3. Create a file django-polls/README.rst with the following contents:

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    django-polls/README.rst
    Code
    =====\nPolls\n=====\n\nPolls is a simple Django app to conduct Web-based polls. For each\nquestion, visitors can choose between a fixed number of answers.\n\nDetailed documentation is in the "docs" directory.\n\nQuick start\n-----------\n\n1. Add "polls" to your INSTALLED_APPS setting like this::\n\n    INSTALLED_APPS = [\n        ...\n        'polls',\n    ]\n\n2. Include the polls URLconf in your project urls.py like this::\n\n    url(r'^polls/', include('polls.urls')),\n\n3. Run `python manage.py migrate` to create the polls models.\n\n4. Start the development server and visit http://127.0.0.1:8000/admin/\n   to create a poll (you'll need the Admin app enabled).\n\n5. Visit http://127.0.0.1:8000/polls/ to participate in the poll.\n
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    4. \n

  4. Create a django-polls/LICENSE file. Choosing a license is beyond the\nscope of this tutorial, but suffice it to say that code released publicly\nwithout a license is useless. Django and many Django-compatible apps are\ndistributed under the BSD license; however, you’re free to pick your own\nlicense. Just be aware that your licensing choice will affect who is able\nto use your code.

    5. \n

  5. Next we’ll create a setup.py file which provides details about how to\nbuild and install the app. A full explanation of this file is beyond the\nscope of this tutorial, but the setuptools docs have a good\nexplanation. Create a file django-polls/setup.py with the following\ncontents:

    \n
    django-polls/setup.py
    Code
    import os\nfrom setuptools import find_packages, setup\n\nwith open(os.path.join(os.path.dirname(__file__), 'README.rst')) as readme:\n    README = readme.read()\n\n# allow setup.py to be run from any path\nos.chdir(os.path.normpath(os.path.join(os.path.abspath(__file__), os.pardir)))\n\nsetup(\n    name='django-polls',\n    version='0.1',\n    packages=find_packages(),\n    include_package_data=True,\n    license='BSD License',  # example license\n    description='A simple Django app to conduct Web-based polls.',\n    long_description=README,\n    url='https://www.example.com/',\n    author='Your Name',\n    author_email='yourname@example.com',\n    classifiers=[\n        'Environment :: Web Environment',\n        'Framework :: Django',\n        'Framework :: Django :: X.Y',  # replace "X.Y" as appropriate\n        'Intended Audience :: Developers',\n        'License :: OSI Approved :: BSD License',  # example license\n        'Operating System :: OS Independent',\n        'Programming Language :: Python',\n        # Replace these appropriately if you are stuck on Python 2.\n        'Programming Language :: Python :: 3',\n        'Programming Language :: Python :: 3.4',\n        'Programming Language :: Python :: 3.5',\n        'Topic :: Internet :: WWW/HTTP',\n        'Topic :: Internet :: WWW/HTTP :: Dynamic Content',\n    ],\n)\n
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    6. \n

  6. Only Python modules and packages are included in the package by default. To\ninclude additional files, we’ll need to create a MANIFEST.in file. The\nsetuptools docs referred to in the previous step discuss this file in more\ndetails. To include the templates, the README.rst and our LICENSE\nfile, create a file django-polls/MANIFEST.in with the following\ncontents:

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    django-polls/MANIFEST.in
    Code
    include LICENSE\ninclude README.rst\nrecursive-include polls/static *\nrecursive-include polls/templates *\n
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    7. \n

  7. It’s optional, but recommended, to include detailed documentation with your\napp. Create an empty directory django-polls/docs for future\ndocumentation. Add an additional line to django-polls/MANIFEST.in:

    \n
    Code
    recursive-include docs *\n
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    Note that the docs directory won’t be included in your package unless\nyou add some files to it. Many Django apps also provide their documentation\nonline through sites like readthedocs.org.

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    8. \n

  8. Try building your package with python setup.py sdist (run from inside\ndjango-polls). This creates a directory called dist and builds your\nnew package, django-polls-0.1.tar.gz.

    9. \n
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For more information on packaging, see Python’s Tutorial on Packaging and\nDistributing Projects.

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Using your own packageLink to this heading#

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Since we moved the polls directory out of the project, it’s no longer\nworking. We’ll now fix this by installing our new django-polls package.

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  1. To install the package, use pip (you already installed it, right?):

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    Code
    pip install --user django-polls/dist/django-polls-0.1.tar.gz\n
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    2. \n

  2. With luck, your Django project should now work correctly again. Run the\nserver again to confirm this.

    3. \n

  3. To uninstall the package, use pip:

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    Code
    pip uninstall django-polls\n
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    4. \n
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Publishing your appLink to this heading#

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Now that we’ve packaged and tested django-polls, it’s ready to share with\nthe world! If this wasn’t just an example, you could now:

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Installing Python packages with virtualenvLink to this heading#

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Earlier, we installed the polls app as a user library. This has some\ndisadvantages:

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Typically, these situations only arise once you’re maintaining several Django\nprojects. When they do, the best solution is to use virtualenv. This tool allows you to maintain multiple\nisolated Python environments, each with its own copy of the libraries and\npackage namespace.

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