What is async/await in Python?

Question

Accepted Answer

**async/await** — syntax for **asynchronous programming**. Allows writing concurrent code that looks synchronous.

**async def** defines a coroutine. **await** pauses execution until the result is ready.

```python
import asyncio

async def fetch_data(url):
    print(f"Start fetching {url}")
    await asyncio.sleep(2)  # Simulate I/O
    return f"Data from {url}"

async def main():
    # Sequential (slow)
    result1 = await fetch_data("api1.com")
    result2 = await fetch_data("api2.com")

# Concurrent (fast)
    task1 = asyncio.create_task(fetch_data("api1.com"))
    task2 = asyncio.create_task(fetch_data("api2.com"))
    result1, result2 = await task1, await task2

asyncio.run(main())
```

**Key rules:**
- `await` only inside `async def`.
- `asyncio.run()` starts the event loop.
- Best for I/O-bound tasks (network, files).

Python: What is async/await in Python?