Django vs FastAPI — when would you choose each, and what are the architectural trade-offs?

Question

At a startup deciding on their Python web framework:

> "We're building a platform with a REST API, admin dashboard, and background job processing. Team has experience with Django. Should we stick with Django or migrate to FastAPI? What are the trade-offs?"

Interview OS Community · Accepted Answer

## Comparison

| Aspect | Django | FastAPI |
|--------|--------|---------|
| **Philosophy** | Batteries included | Minimal, explicit |
| **Async support** | Partial (3.1+) | Native async/await |
| **Performance** | Moderate (~1K req/s) | Fast (~3-5K req/s) |
| **Admin panel** | Built-in, excellent | Manual or third-party |
| **ORM** | Django ORM (powerful) | SQLAlchemy (flexible) |
| **API docs** | Manual (drf-spectacular) | Auto-generated (Swagger) |
| **Learning curve** | Steep (conventions) | Easy (standard Python) |
| **Type safety** | Minimal | Full Pydantic validation |
| **Ecosystem** | Massive (packages) | Growing |
| **Best for** | Content sites, admin-heavy | APIs, microservices |

## Choose Django When:
- Need admin panel (manage users, content, data)
- Building content-heavy sites (CMS, e-commerce)
- Team already knows Django well
- Need ORM migrations + Django ecosystem

## Choose FastAPI When:
- Building pure API / microservice
- Need high performance and async
- Want auto-generated API docs
- Type validation is critical
- Building real-time features (WebSocket)

## Hybrid Approach (Common)

```
Django (monolith):
  - Admin panel, user management, content
  - /admin/ → Django admin
  - /api/v2/ → Django REST Framework

FastAPI (microservice):
  - High-performance API endpoints
  - Real-time features
  - ML model serving
```

## FastAPI Example (type-safe API)

```python
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Application(BaseModel):
    company: str
    position: str
    salary: float | None = None

@app.post("/applications")
async def create_application(app_data: Application):
    # Pydantic validates request body automatically
    return await db.create(app_data)

# Auto-generated Swagger docs at /docs
```

Interview OS

Django vs FastAPI — when would you choose each, and what are the architectural trade-offs?

Question Details

Suggested Solution

Comparison

Choose Django When:

Choose FastAPI When:

Hybrid Approach (Common)

FastAPI Example (type-safe API)

Auto-generated Swagger docs at /docs

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