How do `async` and `await` work?

This repository is a brief exploration of how async and await work in different languages after I noticed that Python and JavaScript do things quite differently in this department.

This simple demo program looks almost the same in the various languages with async and await keywords:

async def return_number_async(n):
    print('in return_number_async')
    return n

async def silly_example():
    print('start of async function')
    fut = return_number_async(10)
    print('called return_number_async(10)')
    n = await fut
    print(f'result: {n}')

if __name__ == '__main__':
    import asyncio
    asyncio.run(silly_example())

The Python version prints:

start of async function
called return_number_async(10)
in return_number_async
result: 10

The JavaScript equivalent prints

start of async function
in return_number_async
called return_number_async(10)
result: 10

.net/C# behaves the same way as JavaScript. Both have a very similar task-based model of async which could be described as ‘eager’ compared to Python’s coroutine-based model. Rust behaves the same way as Python.

For Python, JavaScript and C#, I've also added variants that do the same thing but without language support for async.

tjol/how-does-async-work

How do async and await work?

How do `async` and `await` work?