Django Fix, Crash & Optimization Guide

Django is a high-level Python web framework for building secure, data-driven sites quickly, maintained by the Django Software Foundation. It ships with an ORM, an admin interface, auth, and a built-in dev server.

Install / First Setup

Install and scaffold a project:

pip install django
django-admin startproject myproject
cd myproject
python manage.py runserver

The dev server runs at http://127.0.0.1:8000. Always work inside a virtual environment (python -m venv .venv then activate) to isolate dependencies. Django 4.x/5.x requires Python 3.10+ (verify against your installed Django version).

Common Issues & Fixes

"ModuleNotFoundError: No module named 'django'"

Cause: Django isn't installed in the active interpreter, or the virtualenv isn't activated. Fix: Activate your venv (source .venv/bin/activate on macOS/Linux, .venv\Scripts\activate on Windows) and pip install django.

Migration conflicts / "table already exists"

Cause: Divergent migration files or a DB created outside migrate. Fix: For fake-initial states use python manage.py migrate --fake <app> zero then re-migrate, or makemigrations then migrate. Resolve conflicting migrations by editing/merging them (makemigrations --merge when auto-mergeable).

"DisallowedHost at /"

Cause: The request's Host header isn't in ALLOWED_HOSTS. Fix: Add the host to ALLOWED_HOSTS in settings.py (e.g. ['localhost', '127.0.0.1'] for dev, your domain for prod).

"ImproperlyConfigured: SECRET_KEY not set"

Cause: SECRET_KEY is missing or not loaded from the environment. Fix: Set it via an environment variable and read it in settings.py (e.g. os.environ['SECRET_KEY']); never hardcode secrets in version control.

CSRF verification failed

Cause: A POST form missing the token, or the CSRF cookie blocked. Fix: Include {% csrf_token %} in forms, ensure cookies are enabled, and confirm CSRF_TRUSTED_ORIGINS for cross-origin HTTPS setups.

Performance & Optimization

• Low-End (4–8 GB RAM): Use the default dev server (single-threaded) for development only. Keep the DB local (SQLite for tiny apps, PostgreSQL for realistic loads). Avoid running heavy background workers alongside.
• Mid (16 GB): Use PostgreSQL, enable select_related/prefetch_related to kill N+1 queries, and add django-debug-toolbar to find slow queries. Use cache (local-memory or Redis) for expensive views.
• Workstation (32 GB+): Run a local PostgreSQL + Redis stack, use DB connection pooling (CONN_MAX_AGE), and cache templates/queries aggressively. In production use Gunicorn/uvicorn+gunicorn workers and a reverse proxy (Nginx).

Always run python manage.py check --deploy before production and use the ORM's only()/defer() to limit fetched columns.

Version & Compatibility Notes

• Recent Django releases require Python 3.10 or newer (exact minimum depends on the Django version). Confirm with your installed release.
• Django 5.x dropped support for older Python versions; the async ORM and async views continue to mature.
• The built-in runserver is for development only — never use it in production. For exact version/Python pairings, consult official release notes.

FAQ

Q: How do I fix "table already exists" migration errors? A: Use migrate --fake to mark already-applied migrations without running SQL, or reset and re-migrate in development. Resolve conflicts with makemigrations --merge.

Q: Why do I get DisallowedHost? A: The Host header isn't in ALLOWED_HOSTS. Add your dev host (localhost, 127.0.0.1) or your domain.

Q: Is runserver safe for production? A: No. It is single-threaded and unsecured. Use Gunicorn/uWSGI behind Nginx in production.

Q: How do I fix N+1 queries? A: Use select_related (foreign keys) and prefetch_related (many-to-many/reverse) in your querysets, and profile with django-debug-toolbar.

Q: How do I set SECRET_KEY securely? A: Store it in an environment variable and read it in settings.py; keep it out of source control (use .env + a loader, not committed files).

Q: Which Python version does Django need? A: Recent Django needs Python 3.10+. Check the release notes for your specific Django version.

Related Guides

• Flask Fix & Optimization Guide
• FastAPI Fix & Optimization Guide
• Dev RAM Calculator

Accuracy Note

Commands and paths reflect common, real-world setups as of 2026-08. Always verify against your installed version and OS. When in doubt, consult the official Django documentation.