What is FastAPI background tasks?

Question

Accepted Answer

**FastAPI** provides **BackgroundTasks** for running code after response is sent.

```python
from fastapi import FastAPI, BackgroundTasks
from typing import Optional

app = FastAPI()

def send_email(email: str, message: str):
    # This runs AFTER response is sent
    print(f"Sending email to {email}: {message}")
    # smtp.send(email, message)

def log_action(action: str, user_id: int):
    print(f"User {user_id} performed {action}")

@app.post("/users/")
async def create_user(
    name: str,
    email: str,
    background_tasks: BackgroundTasks
):
    user = User(name=name, email=email)
    db.add(user)
    await db.commit()

# Add background tasks
    background_tasks.add_task(
        send_email,
        email=email,
        message="Welcome!"
    )
    background_tasks.add_task(
        log_action,
        action="create_user",
        user_id=user.id
    )

return {"message": "User created"}

# Task runs in same process, after response
```

**Use cases:**
- Sending emails.
- Logging.
- Updating caches.
- Notifications.

**Limitations:**
- Runs in same process.
- No retry mechanism.
- Use Celery for complex tasks.

Python: What is FastAPI background tasks?