============
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.
One big exception to :pep:`8` is our preference of longer line lengths.
We're well into the 21st Century, and we have high-resolution computer
screens that can fit way more than 79 characters on a screen. Don't limit
lines of code to 79 characters if it means the code looks significantly
uglier or is harder to read.
* 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).
* Use convenience imports whenever available. For example, do this::
from django.views.generic import View
Don't do this::
from django.views.generic.base import View
* 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)
* If you define a ``__str__`` method (previously ``__unicode__`` before Python 3
was supported), decorate the model class with
:func:`~django.utils.encoding.python_2_unicode_compatible`.
* 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 __str__()``
* ``def save()``
* ``def get_absolute_url()``
* Any custom methods
* If ``choices`` is defined for a given model field, define each choice as
a tuple of tuples, with an all-uppercase name as a class attribute on the
model. Example::
class MyModel(models.Model):
DIRECTION_UP = 'U'
DIRECTION_DOWN = 'D'
DIRECTION_CHOICES = (
(DIRECTION_UP, 'Up'),
(DIRECTION_DOWN, 'Down'),
)
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 ``django.utils.functional.LazyObject``,
``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. Note, however, that patches which only
remove whitespace (or only make changes for nominal :pep:`8` conformance)
are likely to be rejected, since they only introduce noise rather than
code improvement. Tidy up when you're next changing code in the area.
* 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: https://pypi.python.org/pypi/pep8
.. _pyflakes: https://pypi.python.org/pypi/pyflakes
.. _pylint: https://pypi.python.org/pypi/pylint
