Django Development Skill

Django Development Skill

When to Use

Use this skill when:

• Writing, reviewing, or refactoring Django applications
• Creating or modifying Django models, views, admin, forms
• Setting up Django project structure and tooling
• Implementing Celery tasks and signals
• Writing Django tests
• Configuring linters (ruff, pylint) for Python/​Django

Prerequisites Check

Before starting any Django work:

# Check Python version
python --version

# Check for .python-version file
cat .python-version 2>/​dev/​null

# Verify virtual environment is active
echo $VIRTUAL_ENV

# Check Django version
python -c "import django; print(django.VERSION)"

# Check if ruff is available
command -v ruff

---

Instructions

General Coding Approach

• All naming and comments must be in English
• Follow Python (PEP 8) and Django conventions
• Virtual environment must be activated
• Detect project's Python version and use appropriate features
• Do not use type annotations (Django doesn't fully rely on them)
• If annotations are needed, import: from __future__ import annotations

---

Formatting and Linting

Ruff Setup

python -m pip install ruff

Minimal .ruff.toml:

line-length = 119
indent-width = 4
target-version = "py312"
exclude = [
    "**/​migrations",
    "**/​manage.py",
]

[format]
quote-style = "single"
exclude = ["**/​manage.py"]

[lint]
select = ["ALL"]
allowed-confusables = ["ı", "'"]
mccabe.max-complexity = 15
ignore = [
    "ANN",    # annotations
    "D",      # docstrings (pydocstyle)
    "D203",   # one-blank-line-before-class
    "D213",   # multi-line-summary-second-line
    "ISC001", # implicit string concat
    "COM812", # missing trailing comma
    "ERA",    # commented out code
    "RUF012", # mutable class default
    "FBT002", # boolean default positional arg
    "TD003",  # missing todo link
    "FIX002", # line contains todo
    "PT009",  # pytest unittest assertion
    "PT019",  # pytest fixture param
    "PT027",  # pytest unittest raises
    "PGH004", # file-wide noqa
    "INP001", # implicit namespace package
]

[lint.flake8-quotes]
inline-quotes = "single"
docstring-quotes = "double"

[lint.pylint]
max-statements = 100
max-returns = 20
max-args = 10
max-positional-args = 8
max-branches = 20

[lint.isort]
known-first-party = ["core"]
section-order = [
    "future",
    "standard-library",
    "django",
    "third-party",
    "first-party",
    "local-folder",
]

[lint.isort.sections]
django = ["django"]

Pylint Setup

python -m pip install pylint

# Generate config if missing
pylint --generate-rcfile > .pylintrc

Acceptable noqa Comments

• # noqa: S324 - hashlib security
• # noqa: SLF001 - Model._meta access
• # noqa: ARG002 - unused args in Django overrides

Always ask before adding other noqa comments.

---

Coding Style

Quote Convention

Always use single quotes. Double quotes only for docstrings or unavoidable cases:

# ✅ Good
user_name = 'vigo'
page = request.GET.get('page')

# ✅ Acceptable
message = "vigo's number"

No Magic Values

# ❌ Bad
def check_age(user):
    if user.age > 10:
        pass

# ✅ Good
USER_MAX_AGE = 10

def check_age(user):
    if user.age > USER_MAX_AGE:
        pass

Dict Access

Always use .get() for dict access:

# ❌ Bad
value = FOO['bar']

# ✅ Good
value = FOO.get('bar')
value = FOO.get('bar', 'default')

Error Handling

Never use blind exceptions. Always handle specific exceptions:

# ❌ Bad
try:
    do_something()
except Exception:
    pass

# ✅ Good
try:
    do_something()
except SpecificError as exc:
    logger.exception('Operation failed: %s', exc)
    raise

Service-Specific Exceptions

Every service must have its own exception:

# exceptions.py
class ProjectError(Exception):
    def __init__(self, message, humans=False, **extras):
        if humans:
            message = message.title()
        super().__init__(message)
        self.humans = humans
        self.message = message
        self.extras = extras


class NotificationServiceError(ProjectError):
    ...


# services/​notification.py
import logging

logger = logging.getLogger('project.NotificationService')


class NotificationService:
    def send(self, recipient, message):
        try:
            response = ExternalAPI.send(recipient, message)
        except ExternalAPIError as exc:
            logger.exception('Failed to send notification')
            raise NotificationServiceError('Notification failed') from exc
        return response

---

Django Project Structure

core/
    admin/
        __init__.py
        user.py
    fixtures/
        core.user.json
    forms/
        __init__.py
        user.py
    management/
        __init__.py
        commands/
            create_foo.py
    migrations/
    models/
        __init__.py
        user.py
    services/
        __init__.py
        notification.py
    signals/
        __init__.py
        user.py
    tasks/
        __init__.py
        notification.py
    templates/
        auth/
            signin.html
    views/
        __init__.py
        auth/
            __init__.py
            login.py
    checks.py
    storage.py

---

AppConfig Example

# pylint: disable=W0611,C0415
# ruff: noqa: F401,PLC0415
from django.apps import AppConfig
from django.conf import settings


class CoreConfig(AppConfig):
    default_auto_field = 'django.db.models.BigAutoField'
    name = 'core'

    def ready(self):
        from .signals import user_signals
        from .tasks import notification_tasks

        if settings.DEBUG:
            from .checks import check_environment_variables, check_models

---

Model Rules

Basic Structure

from django.contrib.auth import get_user_model
from django.db import models
from django.utils.translation import gettext_lazy as _


class PostManager(models.Manager):
    def get_by_natural_key(self, author_email, title):
        author = get_user_model().objects.get_by_natural_key(author_email)
        return self.get(author=author, title=title)


class Post(models.Model):
    # 1. Field declarations
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_('created at'),
    )
    updated_at = models.DateTimeField(
        auto_now=True,
        verbose_name=_('updated at'),
    )
    title = models.CharField(
        max_length=255,
        verbose_name=_('title'),
    )
    body = models.TextField(
        blank=True,
        verbose_name=_('body'),
    )
    author = models.ForeignKey(
        to=get_user_model(),
        related_name='posts',
        related_query_name='post',
        on_delete=models.CASCADE,
        verbose_name=_('author'),
    )

    # 2. Custom managers
    objects = PostManager()

    # 3. Class Meta
    class Meta:
        app_label = 'core'
        db_table = 'post'
        verbose_name = _('Post')
        verbose_name_plural = _('Posts')

    # 4. __str__
    def __str__(self):
        return f'{self.title}'

    # 5. save (if needed)

    # 6. natural_key
    def natural_key(self):
        return (self.author.email, self.title)

    natural_key.dependencies = ['auth.user']

    # 7. get_absolute_url (if needed)

Model Method Order

1. Field declarations
2. Custom managers
3. class Meta
4. __str__
5. save
6. natural_key
7. get_absolute_url

Model Checklist

Choices

Use callable for choices (allows changes without migration):

def get_language_choices():
    return settings.LANGUAGES


class Page(models.Model):
    language = models.CharField(
        max_length=2,
        choices=get_language_choices,
        verbose_name=_('language'),
    )

Or use Django's TextChoices:

class LanguageChoices(models.TextChoices):
    ENGLISH = 'en', _('English')
    TURKISH = 'tr', _('Turkish')

Or stdlib Enum:

from enum import StrEnum


class CandidateStatus(StrEnum):
    STARTED = 'started'
    IN_PROGRESS = 'in_progress'
    COMPLETED = 'completed'

Constraints and Indexes

class Meta:
    constraints = [
        models.UniqueConstraint(
            fields=['name', 'owner'],
            condition=models.Q(owner__isnull=False),
            name='uc_org_name_owner',  # uc_<identifier>_<field>
        ),
    ]
    indexes = [
        models.Index(
            fields=['candidate_name'],
            condition=~models.Q(candidate_name=''),
            name='idx_cand_name',  # idx_<identifier>_<field>
        ),
    ]

File Upload Fields

from django.core.files.storage import FileSystemStorage


def dynamic_file_storage():
    return FileSystemStorage()


def upload_video_path(instance, filename):
    return f'videos/​{instance.pk}/​{filename}'


class Media(models.Model):
    video = models.FileField(
        upload_to=upload_video_path,
        storage=dynamic_file_storage,
        verbose_name=_('video'),
    )

---

Admin Rules

Admin files live in <app>/​admin/<model>.py:

from django.contrib import admin

from core.admin.base import BaseModelAdmin
from core.models import Post


@admin.register(Post)
class PostAdmin(BaseModelAdmin):
    list_display = ('title', 'author', 'created_at')
    list_display_links = ('title',)
    search_fields = ('title', 'body')
    ordering = ('-created_at',)

    # Performance for ForeignKey fields
    autocomplete_fields = ('author',)
    list_select_related = ('author',)

Minimum Admin Properties

• list_display
• list_display_links
• search_fields
• ordering

For ForeignKey fields, always add:

• autocomplete_fields
• list_select_related

---

View Rules

• Views live in <app>/​views/
• Only Class-Based Views (no function-based views)
• Separate business logic into service layer

# ❌ Bad - logic in view
class OrderView(View):
    def post(self, request):
        # 50 lines of business logic here
        ...


# ✅ Good - logic in service
class OrderView(View):
    def post(self, request):
        form = self.get_form()
        if not form.is_valid():
            return self.form_invalid(form)

        service = OrderService(
            request=request,
            form=form,
            logger=self.logger,
        )
        redirect_url = service.process_order()
        return HttpResponseRedirect(redirect_url)

---

Internationalization

Never use hardcoded strings:

# ❌ Bad
return HttpResponse('Error')

# ✅ Good
from django.utils.translation import gettext_lazy as _

return HttpResponse(_('Error'))

In templates:

{% load i18n %}

{% translate "Welcome" %}

{% blocktranslate with name=user.name %}
Hello, {{ name }}!
{% endblocktranslate %}

---

Celery Tasks

Tasks live in <app>/​tasks/:

# tasks/​notification.py
from celery import shared_task

from core.services.notification import NotificationService, NotificationServiceError


@shared_task(
    bind=True,
    max_retries=3,
    default_retry_delay=60,
)
def send_notification_task(self, user_id, message):
    try:
        service = NotificationService()
        service.send(user_id, message)
    except NotificationServiceError as exc:
        self.retry(exc=exc)

Register in AppConfig.ready():

def ready(self):
    from .tasks import notification  # noqa: F401

---

Testing

Tests live in tests/ directory:

tests/
    test_models_post.py
    test_views_auth.py
    test_services_notification.py
    test_forms_user.py
    test_tasks_notification.py

Naming convention: test_<type>_<name>.py

Use stdlib and Django's test suites:

from django.test import TestCase


class PostModelTest(TestCase):
    def test_str_returns_title(self):
        post = Post(title='Hello')
        self.assertEqual(str(post), 'Hello')

---

Django System Checks

Create checks.py for custom checks:

# pylint: disable=W0613
# ruff: noqa: ARG001,SLF001
import ast
import inspect
import os

import django.apps
from django.core import checks
from django.core.exceptions import FieldDoesNotExist

DEVELOPMENT_ENVIRONMENT_VARIABLES = [
    'DJANGO_SECRET_KEY',
    'DATABASE_URL',
    # other required environment variable name
]

FIELD_VERBOSE_NAME_WHITE_LIST = ['slug']
# MODEL_NAME_WHITE_LIST = [foomodel']


@checks.register()
def check_environment_variables(app_configs, **kwargs):
    errors = []
    for var_name in DEVELOPMENT_ENVIRONMENT_VARIABLES:
        if not os.environ.get(var_name):
            errors = [
                *errors,
                checks.Error(
                    f'Missing environment variable for development: {var_name}',
                    hint=f'Set the "{var_name}" environment variable in your environment.',
                    id='core.ENV001',
                ),
            ]
    return errors


def check_model_get_argument(node, arg):
    for kw in node.value.keywords:
        if kw.arg == arg:
            return kw
    return None


def check_model_is_gettext_node(node):
    if not isinstance(node, ast.Call):
        return False

    return node.func.id == '_'


def check_model_get_field(model, node):
    if not isinstance(node, ast.Assign):
        return None
    if len(node.targets) != 1:
        return None
    if not isinstance(node.targets[0], ast.Name):
        return None
    try:
        return model._meta.get_field(node.targets[0].id)
    except FieldDoesNotExist:
        return None


def check_model_fields_verbose_name(field, node):
    verbose_name = check_model_get_argument(node, 'verbose_name')
    if field.name not in FIELD_VERBOSE_NAME_WHITE_LIST:
        if verbose_name is None:
            yield checks.Warning(
                'Field has no verbose name',
                hint='Set verbose name on the field.',
                obj=field,
                id='BLT001',
            )
        elif not check_model_is_gettext_node(verbose_name.value):
            yield checks.Warning(
                'Verbose name should use gettext _() style',
                hint='Use gettext on the verbose name.',
                obj=field,
                id='BLT002',
            )


def check_model_class_meta(class_meta, model):
    if class_meta is None:
        yield checks.Warning(
            f'Model "{model._meta.model_name}" must define class Meta',
            hint=f'Add class Meta to model "{model._meta.model_name}".',
            obj=model,
            id='BLT003',
        )
    else:
        verbose_name = None
        verbose_name_plural = None

        for node in ast.iter_child_nodes(class_meta):
            if not isinstance(node, ast.Assign):
                continue

            if not isinstance(node.targets[0], ast.Name):
                continue

            attr = node.targets[0].id

            if attr == 'verbose_name':
                verbose_name = node

            if attr == 'verbose_name_plural':
                verbose_name_plural = node

        if verbose_name is None:
            yield checks.Warning(
                'Model has no verbose name',
                hint='Add verbose_name to class Meta.',
                obj=model,
                id='BLT004',
            )

        elif not check_model_is_gettext_node(verbose_name.value):
            yield checks.Warning(
                'Verbose name in class Meta should use gettext',
                hint=f'Use gettext on the verbose_name of class Meta "{model._meta.model_name}".',
                obj=model,
                id='BLT002',
            )

        if verbose_name_plural is None:
            yield checks.Warning(
                'Model has no verbose name plural',
                hint='Add verbose_name_plural to class Meta.',
                obj=model,
                id='BLT005',
            )

        elif not check_model_is_gettext_node(verbose_name_plural.value):
            yield checks.Warning(
                'Verbose name plural in class Meta should use gettext',
                hint=f'Use gettext on the verbose_name_plural of class Meta "{model._meta.model_name}".',
                obj=model,
                id='BLT002',
            )


def check_model(model):
    """

    BLT001: Field has no verbose name.
    BLT002: Verbose name should use gettext.
    BLT003: Model must define class Meta.
    BLT004: Model has no verbose name.
    BLT005: Model has no verbose name plural.

    """
    if model._meta.model_name not in MODEL_NAME_WHITE_LIST:
        model_source = inspect.getsource(model)
        model_node = ast.parse(model_source)
        class_meta = None
        for node in model_node.body[0].body:
            if isinstance(node, ast.ClassDef) and node.name == 'Meta':
                class_meta = node

            field = check_model_get_field(model, node)
            if field is None:
                continue

            yield from check_model_fields_verbose_name(field, node)

        yield from check_model_class_meta(class_meta, model)


@checks.register(checks.Tags.models)
def check_models(app_configs, **kwargs):
    errors = []
    for app in django.apps.apps.get_app_configs():
        if app.path.find('site-packages') > -1:
            continue

        for model in app.get_models():
            for check_message in check_model(model):
                errors = [*errors, check_message]
    return errors

---

Pre-Commit Hooks

brew install pre-commit
pre-commit install

Minimal .pre-commit-config.yaml:

exclude: core/​migrations/
fail_fast: true
repos:
  - repo: local
    hooks:
      - id: django-check
        name: Django checks
        entry: scripts/​pre-commit/​django-check.bash
        language: script
        always_run: true
        pass_filenames: false

      - id: ruff
        name: Ruff linter
        entry: ruff check .
        language: system
        types: [python]

      - id: pylint
        name: Pylint check
        entry: pylint -rn -sn -d R0401 config core
        language: system
        types: [python]

      - id: django-test
        name: Django tests
        entry: scripts/​pre-commit/​run-tests.bash
        language: system
        types: [python]
        pass_filenames: false

scripts/​pre-commit/​django-check.bash:

#!/​usr/​bin/​env bash
set -euo pipefail

DJANGO_ENV=production python manage.py check --deploy || exit 0

scripts/​pre-commit/​run-tests.bash:

#!/​usr/​bin/​env bash
set -euo pipefail

coverage run manage.py test --failfast

---

Commit Messages

Format:

[claude]: <verb> <description in lowercase>

- Detail 1
- Detail 2

Fixes #123

🤖 Generated with [Claude Code](https://claude.ai/​code)
Co-Authored-By: Claude <[email protected]>

Example:

[claude]: add user notification service

- Implement NotificationService with retry logic
- Add NotificationServiceError for error handling
- Create Celery task for async notifications

Fixes #42

🤖 Generated with [Claude Code](https://claude.ai/​code)
Co-Authored-By: Claude <[email protected]>

---

Quick Reference

---

Resources

• Django Documentation
• Ruff Documentation
• Pylint Documentation
• Celery Documentation