django/docs/internals/contributing/writing-code/coding-style.txt

============
Coding Style
============

Please follow these coding standards when writing code for inclusion in Django.

Python style
------------

    * Unless otherwise specified, follow :pep:`8`.

      You could use a tool like `pep8`_ to check for some problems in this
      area, but remember that PEP 8 is only a guide, so respect the style of
      the surrounding code as a primary goal.

    * Use four spaces for indentation.

    * Use underscores, not camelCase, for variable, function and method names
      (i.e. ``poll.get_unique_voters()``, not ``poll.getUniqueVoters``).

    * Use ``InitialCaps`` for class names (or for factory functions that
      return classes).

    * In docstrings, use "action words" such as::

          def foo():
              """
              Calculates something and returns the result.
              """
              pass

      Here's an example of what not to do::

          def foo():
              """
              Calculate something and return the result.
              """
              pass

Template style
--------------

    * In Django template code, put one (and only one) space between the curly
      brackets and the tag contents.

      Do this:

      .. code-block:: html+django

          {{ foo }}

      Don't do this:

      .. code-block:: html+django

          {{foo}}

View style
----------

    * In Django views, the first parameter in a view function should be called
      ``request``.

      Do this::

          def my_view(request, foo):
              # ...

      Don't do this::

          def my_view(req, foo):
              # ...

Model style
-----------

    * Field names should be all lowercase, using underscores instead of
      camelCase.

      Do this::

          class Person(models.Model):
              first_name = models.CharField(max_length=20)
              last_name = models.CharField(max_length=40)

      Don't do this::

          class Person(models.Model):
              FirstName = models.CharField(max_length=20)
              Last_Name = models.CharField(max_length=40)

    * The ``class Meta`` should appear *after* the fields are defined, with
      a single blank line separating the fields and the class definition.

      Do this::

          class Person(models.Model):
              first_name = models.CharField(max_length=20)
              last_name = models.CharField(max_length=40)

              class Meta:
                  verbose_name_plural = 'people'

      Don't do this::

          class Person(models.Model):
              first_name = models.CharField(max_length=20)
              last_name = models.CharField(max_length=40)
              class Meta:
                  verbose_name_plural = 'people'

      Don't do this, either::

          class Person(models.Model):
              class Meta:
                  verbose_name_plural = 'people'

              first_name = models.CharField(max_length=20)
              last_name = models.CharField(max_length=40)

    * The order of model inner classes and standard methods should be as
      follows (noting that these are not all required):

        * All database fields
        * Custom manager attributes
        * ``class Meta``
        * ``def __unicode__()``
        * ``def __str__()``
        * ``def save()``
        * ``def get_absolute_url()``
        * Any custom methods

    * If ``choices`` is defined for a given model field, define the choices as
      a tuple of tuples, with an all-uppercase name, either near the top of
      the model module or just above the model class. Example::

          GENDER_CHOICES = (
              ('M', 'Male'),
              ('F', 'Female'),
          )

Use of ``django.conf.settings``
-------------------------------

Modules should not in general use settings stored in ``django.conf.settings``
at the top level (i.e. evaluated when the module is imported). The explanation
for this is as follows:

Manual configuration of settings (i.e. not relying on the
``DJANGO_SETTINGS_MODULE`` environment variable) is allowed and possible as
follows::

    from django.conf import settings

    settings.configure({}, SOME_SETTING='foo')

However, if any setting is accessed before the ``settings.configure`` line,
this will not work. (Internally, ``settings`` is a ``LazyObject`` which
configures itself automatically when the settings are accessed if it has not
already been configured).

So, if there is a module containing some code as follows::

    from django.conf import settings
    from django.core.urlresolvers import get_callable

    default_foo_view = get_callable(settings.FOO_VIEW)

...then importing this module will cause the settings object to be configured.
That means that the ability for third parties to import the module at the top
level is incompatible with the ability to configure the settings object
manually, or makes it very difficult in some circumstances.

Instead of the above code, a level of laziness or indirection must be used, such
as :class:`django.utils.functional.LazyObject`,
:func:`django.utils.functional.lazy` or ``lambda``.

Miscellaneous
-------------

    * Mark all strings for internationalization; see the :doc:`i18n
      documentation </topics/i18n/index>` for details.

    * Remove ``import`` statements that are no longer used when you change code.
      The most common tools for this task are `pyflakes`_ and `pylint`_.

    * Systematically remove all trailing whitespaces from your code as those
      add unnecessary bytes, add visual clutter to the patches and can also
      occasionally cause unnecessary merge conflicts. Some IDE's can be
      configured to automatically remove them and most VCS tools can be set to
      highlight them in diff outputs.

    * Please don't put your name in the code you contribute. Our policy is to
      keep contributors' names in the ``AUTHORS`` file distributed with Django
      -- not scattered throughout the codebase itself. Feel free to include a
      change to the ``AUTHORS`` file in your patch if you make more than a
      single trivial change.

.. _pep8: http://pypi.python.org/pypi/pep8
.. _pyflakes: http://pypi.python.org/pypi/pyflakes
.. _pylint: http://pypi.python.org/pypi/pylint