Async Programming (asyncio & await)

import asyncio

# Async function (coroutine)
async def fetch_data(url, delay):
    print(f"  Fetching {url}...")
    await asyncio.sleep(delay * 0.01)  # non-blocking!
    print(f"  Done: {url}")
    return f"Data from {url}"

# Run single coroutine
async def main():
    result = await fetch_data("api/users", 1)
    print(f"  Result: {result}")

asyncio.run(main())

# Run multiple coroutines concurrently
async def main_concurrent():
    tasks = [
        fetch_data("api/users", 2),
        fetch_data("api/posts", 3),
        fetch_data("api/comments", 1),
    ]
    results = await asyncio.gather(*tasks)
    print(f"  All results: {results}")

print("\n--- Concurrent ---")
asyncio.run(main_concurrent())

# Async context manager
class AsyncDB:
    async def __aenter__(self):
        print("  Connecting to DB...")
        await asyncio.sleep(0.01)
        return self
    
    async def __aexit__(self, *args):
        print("  Disconnected.")
    
    async def query(self, sql):
        await asyncio.sleep(0.01)
        return [{"id": 1, "name": "Alice"}]

async def use_db():
    async with AsyncDB() as db:
        result = await db.query("SELECT * FROM users")
        print(f"  Query result: {result}")

print("\n--- Async DB ---")
asyncio.run(use_db())