FastAPI Background Tasks and Async Endpoints

from fastapi import FastAPI, BackgroundTasks, status
from pydantic import EmailStr
import time

app = FastAPI()

def send_welcome_email(email: str):
    # This runs AFTER the client receives the JSON response
    # Note: Using synchronous sleep here is fine because this 
    # specific task is offloaded to a thread by FastAPI
    time.sleep(2) 
    print(f"[TheCodeForge-Worker] Welcome email dispatched to {email}")

@app.post('/register', status_code=status.HTTP_201_CREATED)
async def register_user(email: EmailStr, tasks: BackgroundTasks):
    """
    Registers a user and triggers a background email task.
    The client latency remains low regardless of the email provider speed.
    """
    # 1. Logic to save user to database would go here
    
    # 2. Add the background task
    tasks.add_task(send_welcome_email, email)
    
    return {"status": "success", "detail": "User created. Email is being processed."}

from fastapi import FastAPI
import asyncio
import httpx

app = FastAPI()

# CASE 1: Async Def (Use for Async I/O)
@app.get('/weather/{city}')
async def get_weather(city: str):
    """Standard non-blocking I/O using httpx."""
    async with httpx.AsyncClient() as client:
        response = await client.get(f'https://api.thecodeforge.io/v1/weather/{city}')
        return response.json()

# CASE 2: Regular Def (Use for Sync I/O or CPU work)
@app.get('/hash-password')
def compute_sync_task(password: str):
    """
    FastAPI detects 'def' and runs this in a ThreadPoolExecutor.
    This prevents a CPU-heavy task from stopping the event loop.
    """
    return {"hash": f"hashed_{password}"} # Simulate CPU work

# CASE 3: The 'Loop Killer' (NEVER DO THIS)
# @app.get('/critical-error')
# async def stop_the_world():
#    import time
#    time.sleep(10) # DANGER: Every single user is now waiting 10 seconds