Async layer

Set up data flow with async/await and aiohttp.

Async layer

The second layer uses asyncio.gather to fetch from multiple sources concurrently. gather awaits all the coroutines it receives and returns their results as a list.

async def fetch_all():
    return await asyncio.gather(
        fetch_tasks(), fetch_tasks()
    )

Here fetch_tasks is called twice; gather runs them concurrently. In the real world this is like querying two HTTP sources in parallel; the total time is the slowest call.

gather and await

gather returns a coroutine; you need await to get the result. Without await you keep a coroutine object; the function's result is never obtained.

async def fetch_all():
    return await asyncio.gather(
        fetch_tasks(), fetch_tasks()
    )

Each call is a separate source; gather returns when all of them finish. This pattern is the core advantage of async for speeding up many I/O jobs.

Exercise Add the fetch_all function

The starting code contains the previous lesson's fetch_tasks solution. Add an async def fetch_all(): function whose body does return await asyncio.gather(fetch_tasks(), fetch_tasks()). Then print the result with print(asyncio.run(fetch_all())).

Show example solution

import asyncio

async def fetch_tasks():
    return [{"id": 1, "title": "Görev 1"}, {"id": 2, "title": "Görev 2"}]

async def fetch_all():
    return await asyncio.gather(fetch_tasks(), fetch_tasks())

print(asyncio.run(fetch_all()))

Test yourself

What does asyncio.gather(fetch_tasks(), fetch_tasks()) return?
- A list of two lists
- A single list
- A coroutine
- An error
Show answer

A list of two lists — gather puts each call's result in order; two lists come back.

Complete the gather call

async def fetch_all():
    return await asyncio.____(fetch_tasks(), fetch_tasks())

Show answer

async def fetch_all():
    return await asyncio.gather(fetch_tasks(), fetch_tasks())

Match the async layer concepts

gather

Awaits concurrently
await

Unwraps the result
fetch_all

Multi-source function
asyncio.run

Starts the event loop

Next lesson: SQLAlchemy layer

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