Async IO and Futures in Python: What's the Difference?

Asynchronous programming has become increasingly popular in Python. Two key concepts for async are asyncio and futures. But what exactly is the difference between the two?

Async IO: Asynchronous I/O Made Easy

The asyncio module is used to write asynchronous code in Python. It provides infrastructure for writing async/await code that looks synchronous but allows other tasks to run while one is waiting for I/O.

Some key features of asyncio:

For example:

import asyncio

async def fetch_data():
  print('fetching...')
  await asyncio.sleep(2) # pause for 2 seconds
  print('done!')

async def main():
  await fetch_data()

asyncio.run(main())

This allows other tasks to run while fetch_data pauses for 2 seconds, enabling asynchronous concurrency.

Futures: Managing Promise of a Result

A future represents an eventual result of an asynchronous operation. They provide a way to indirectly wait for and get the result of a long running operation.

Some key aspects of futures:

For example:

from concurrent.futures import Future

f = Future()

def resolve_future():
  print('resolving future...')
  f.set_result('future is done!')

f.add_done_callback(lambda x: print(x.result()))

resolve_future()

So in summary, asyncio provides infrastructure for async I/O concurrency while futures represent eventual results of asynchronous operations. The two concepts work together nicely in the async world!