Python web framework
Models, views, templates, ORM, and Django REST Framework assignments. The top grading deduction on CS50W projects is N+1 query patterns from forgetting select_related, the exact pitfall our tutors annotate with EXPLAIN ANALYZE output. Verified CS graduates from Georgia Tech, BITS Pilani, and Purdue, starting at $20 per task, 12-hour average turnaround.
About
Django is a high-level Python web framework that ships with an ORM, an admin interface, a templating language, a forms library, an authentication system, and migrations infrastructure in the base install. The 5.x release line requires Python 3.10 minimum, supports PostgreSQL 13+ as the primary recommended database, and uses async-capable views alongside the historical sync request-response cycle. Students meet Django in CS50W (Harvard Web Programming), CS41 (Stanford Hap.py Code), Coursera Django for Everybody, and university web development electives that pick Python over Node.
The framework follows the MVT pattern (Model, View, Template) rather than MVC: a URL routes to a view function or class, the view queries models through the ORM, and the view renders a template into HTML or returns JsonResponse for API endpoints. Django REST Framework (DRF) sits on top of the base framework and adds Serializers, ViewSets, Routers, and authentication backends for building HTTP APIs. CSHH tutors deliver models with explicit on_delete cascades, querysets optimized with select_related for foreign keys and prefetch_related for reverse relations, DRF serializers with nested representations and validation, custom permission classes for endpoint-level authorization, and pytest-django test suites covering happy path plus boundary cases.
Common deployment targets in coursework: Heroku (deprecated free tier replaced by Render or Railway), PythonAnywhere, and Docker containers behind Gunicorn.
Coursework
The canonical first Django project. Custom User model extending AbstractUser, Post and Comment models with ForeignKey to User and Post, ModelForm for post creation, function-based views or class-based ListView and DetailView, login_required decorator on edit endpoints, and pagination with Paginator. Tutors include 8 pytest cases covering anonymous read, authenticated write, comment threading, and 404 on missing posts.
Course, Section, and Enrollment models with proper unique_together constraints, ModelSerializer with nested SectionSerializer, ViewSet with @action for custom endpoints (POST /sections/{id}/enroll/), DefaultRouter for URL registration, TokenAuthentication or JWTAuthentication, and IsAuthenticatedOrReadOnly permission. Tutors include APIClient tests for 200, 201, 400, 401, and 403 cases.
Product, Supplier, and StockMovement models registered to django.contrib.admin with custom ModelAdmin classes: list_display, list_filter, search_fields, readonly_fields, and inline editing of stock movements within the product admin page. Tutors customize the admin index, add custom actions for bulk operations, and tighten Permission flags so warehouse staff see only inventory, not user management.
Cart, Order, and OrderItem models with proper status transitions (cart, pending, paid, shipped, refunded), stripe.checkout.Session creation in a view, webhook endpoint with HMAC signature verification, and idempotent order fulfillment that handles duplicate webhook deliveries. Tutors include sandbox API key configuration and pytest mocks of the Stripe SDK.
Thread and Post models with PostgreSQL-specific SearchVector field, SearchQuery and SearchRank for ranking, GIN index on the search_vector column for sub-millisecond lookups, and update_search_vector signal on post save. Tutors include EXPLAIN ANALYZE output showing the GIN index in use versus a sequential scan.
WebSocket consumer extending AsyncWebsocketConsumer, channel layer backed by Redis for group broadcasts, daphne or uvicorn as the ASGI server, JavaScript client using the native WebSocket API. Tutors include integration tests using WebsocketCommunicator from channels.testing.
Celery worker for async tasks (email sending, image processing, periodic reports), Redis as the broker and result backend, @shared_task decorator on task functions, Celery Beat for scheduled jobs (crontab(minute=0, hour=2) for nightly runs). Tutors include CELERY_TASK_ALWAYS_EAGER=True in test settings so tasks execute inline during pytest runs.
Debugging
posts = Post.objects.all()[:100]
for post in posts:
# one extra query PER post: 101 queries total
print(post.author.username)posts = Post.objects.select_related("author")[:100]
for post in posts:
# one query total, JOIN on author_id
print(post.author.username)# chained assignment, fires SettingWithCopyWarning,
# silently fails to mutate the original DataFrame
df[df["a"] > 0]["b"] = 1df.loc[df["a"] > 0, "b"] = 1
# single .loc call mutates df regardless of view/copy statusTwo developers create 0005_add_field.py and 0005_remove_field.py independently, and the next runner gets InconsistentMigrationHistory. Run python manage.py makemigrations --merge to generate a 0006_merge_xxxx.py that depends on both 0005s, then commit. Avoid in production by enforcing a single migration-touching branch at a time.
A form POST returns 403 because the {% csrf_token %} template tag was not included in the form, or the AJAX request did not send the X-CSRFToken header. For HTML forms, drop the tag inside <form>. For DRF API requests, either use SessionAuthentication with the CSRF cookie, switch to TokenAuthentication or JWT (which exempts CSRF), or apply @csrf_exempt to the view (last resort, only for webhook receivers with their own signature verification).
Django templates by default fail silently when a variable does not exist, rendering an empty string. Set TEMPLATES.OPTIONS.string_if_invalid = "INVALID: %s" in settings.py during development to surface every missing variable. Common cause: passing context dict {"posts": qs} but the template uses {{ post.title }} singular instead of {% for post in posts %}.
DEBUG=True serves staticfiles via runserver; DEBUG=False expects the web server to serve them. Run python manage.py collectstatic to gather files into STATIC_ROOT, then configure Nginx or Whitenoise to serve that directory. With Whitenoise, add it to MIDDLEWARE right after SecurityMiddleware and set STATICFILES_STORAGE = "whitenoise.storage.CompressedManifestStaticFilesStorage".
Two concurrent requests check if a slug exists, both see it does not, both insert, and the second one raises IntegrityError because the database unique constraint catches the duplicate. Fix by wrapping the get-or-create logic in a transaction with select_for_update, or using get_or_create which handles the race internally with a single INSERT...ON CONFLICT statement.
USE_TZ=True stores datetimes in UTC; comparing against a naive datetime.now() raises a RuntimeWarning and gives wrong results in queries. Use django.utils.timezone.now() everywhere, and convert at the boundary if data arrives naive. Database column defaults to timestamp with time zone in PostgreSQL when USE_TZ=True.
Code Examples
class Post(models.Model):
title = models.CharField(max_length=200)
author = models.ForeignKey(User, on_delete=models.CASCADE)
body = models.TextField()
created = models.DateTimeField(auto_now_add=True)
class Meta:
indexes = [models.Index(fields=["-created"])]
def feed(request):
# select_related collapses 101 queries into 1 for a 100-post page
qs = Post.objects.select_related("author").order_by("-created")[:25]
return render(request, "feed.html", {"posts": qs})class CommentSerializer(serializers.ModelSerializer):
class Meta:
model = Comment
fields = ["id", "body", "created"]
class PostSerializer(serializers.ModelSerializer):
comments = CommentSerializer(many=True, read_only=True)
author = serializers.ReadOnlyField(source="author.username")
class Meta:
model = Post
fields = ["id", "title", "body", "author", "comments"]Related
FAQ
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