Please follow these coding standards when writing code for inclusion in Django.
Please conform to the indentation style dictated in the .editorconfig file. We recommend using a text editor with EditorConfig support to avoid indentation and whitespace issues. The Python files use 4 spaces for indentation and the HTML files use 2 spaces.
Unless otherwise specified, follow PEP 8.
Use flake8 to check for problems in this area. Note that our setup.cfg file contains some excluded files (deprecated modules we don’t care about cleaning up and some third-party code that Django vendors) as well as some excluded errors that we don’t consider as gross violations. Remember that PEP 8 is only a guide, so respect the style of the surrounding code as a primary goal.
An exception to PEP 8 is our rules on line lengths. Don’t limit lines of code to 79 characters if it means the code looks significantly uglier or is harder to read. We allow up to 119 characters as this is the width of GitHub code review; anything longer requires horizontal scrolling which makes review more difficult. This check is included when you run flake8. Documentation, comments, and docstrings should be wrapped at 79 characters, even though PEP 8 suggests 72.
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, follow PEP 257. For example:
def foo():
"""
Calculate something and return the result.
"""
...
Use isort to automate import sorting using the guidelines below.
Quick start:
$ pip install isort
$ isort -rc .
This runs isort recursively from your current directory, modifying any files that don’t conform to the guidelines. If you need to have imports out of order (to avoid a circular import, for example) use a comment like this:
import module # isort:skip
Put imports in these groups: future, standard library, third-party libraries, other Django components, local Django component, try/excepts. Sort lines in each group alphabetically by the full module name. Place all import module statements before from module import objects in each section. Use absolute imports for other Django components and relative imports for local components.
On each line, alphabetize the items with the upper case items grouped before the lower case items.
Break long lines using parentheses and indent continuation lines by 4 spaces. Include a trailing comma after the last import and put the closing parenthesis on its own line.
Use a single blank line between the last import and any module level code, and use two blank lines above the first function or class.
For example (comments are for explanatory purposes only):
# future
from __future__ import unicode_literals
# standard library
import json
from itertools import chain
# third-party
import bcrypt
# Django
from django.http import Http404
from django.http.response import (
Http404, HttpResponse, HttpResponseNotAllowed, StreamingHttpResponse,
cookie,
)
# local Django
from .models import LogEntry
# try/except
try:
import pytz
except ImportError:
pytz = None
CONSTANT = 'foo'
class Example(object):
# ...
Use convenience imports whenever available. For example, do this:
from django.views.generic import View
instead of:
from django.views.generic.base import View
In Django template code, put one (and only one) space between the curly brackets and the tag contents.
Do this:
{{ foo }}
Don’t do this:
{{foo}}
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):
# ...
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 python_2_unicode_compatible().
The order of model inner classes and standard methods should be as follows (noting that these are not all required):
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'),
)
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.
For details about the JavaScript code style used by Django, see JavaScript.
Mar 31, 2016