9.2. AsyncIO About

• asyncio in Python standard library

• async and await builtin keywords

• Running asynchronously: 3s + 1s + 1s = bit over 3s [execution time]

• Async is the future of programming

9.2.1. Advantages

• Maximize the usage of a single thread

• Handling I/O asynchronously

• Enabling concurrent code using coroutines

• Async will fill the gaps, otherwise wasted on waiting for I/O

• You control when tasks switches occur, so locks and other synchronization are no longer needed

• Async is the cheapest way to task switch

• Cost task switches is incredibly low; calling a pure Python function has more overhead than restarting a generator or awaitable

• Function builds stack each time it's called, whereas async uses generators underneath, which already has stack created

• In terms of speed async servers blows threaded servers in means of thousands

• Async is very cheap in means of resources

• Async world has a huge ecosystem of support tools

• Coding is easier to get right, than threads

9.2.2. Disadvantages

• Async switches cooperatively, so you do need to add explicit code yield or await to cause a task to switch

• Everything you do need a non-blocking version (for example open())

• Increased learning curve

• Create event loop, acquire, crate non-blocking versions of your code

• You think you know Python, there is a second half to learn (async)

9.2.3. Sync vs Async

Figure 9.5. Source: Michael Kennedy 1

Figure 9.6. Source: Michael Kennedy 1

Figure 9.7. Source: Langa, Ł. import asyncio: Learn Python's AsyncIO 4

Figure 9.8. Source: Langa, Ł. import asyncio: Learn Python's AsyncIO 4

9.2.4. Execution

Figure 9.9. Source: Michael Kennedy 1

Figure 9.10. Source: Michael Kennedy 1

9.2.5. Example

>>> import asyncio
>>>
>>>
>>> async def a():
...     print('a: started')
...     await asyncio.sleep(0.2)
...     print('a: finished')
...     return 'a'
>>>
>>> async def b():
...     print('b: started')
...     await asyncio.sleep(0.1)
...     print('b: finished')
...     return 'b'
>>>
>>> async def c():
...     print('c: started')
...     await asyncio.sleep(0.3)
...     print('c: finished')
...     return 'c'
>>>
>>> async def main():
...     result = await asyncio.gather(a(), b(), c())
...     print(f'Result: {result}')
>>>
>>>
>>> asyncio.run(main())
a: started
b: started
c: started
b: finished
a: finished
c: finished
Result: ['a', 'b', 'c']

9.2.6. Further Reading

• Kennedy, M. Demystifying Python's Async and Await Keywords 1

• Kennedy, M. Async Techniques and Examples in Python 2

• Abdalla, A. Creating a Bittorrent Client using Asyncio 3

• Langa, Ł. import asyncio: Learn Python's AsyncIO 4

9.2.7. References

1(1,2,3,4,5)

Kennedy, M. Demystifying Python's Async and Await Keywords. Publisher: JetBrainsTV. Year: 2019. Retrieved: 2022-03-10. URL: https://www.youtube.com/watch?v=F19R_M4Nay4

2

Kennedy, M. Async Techniques and Examples in Python Course. Publisher: TalkPython. Year: 2022. Retrieved: 2022-03-10. URL: https://talkpython.fm/async

3

Abdalla, A. Creating a Bittorrent Client using Asyncio. Year: 2017. Retrieved: 2022-03-10. URL: https://www.youtube.com/watch?v=Pe3b9bdRtiE

4(1,2,3)

Langa, Ł. import asyncio: Learn Python's AsyncIO. Year: 2020. Retrieved: 2022-03-10. URL: https://www.youtube.com/playlist?list=PLhNSoGM2ik6SIkVGXWBwerucXjgP1rHmB