YXYxogenium·Feb 10, 2019
On a related note, I found that asyncio (cooperative multitasking in Python) has made huge strides in usability in Python 3.7. The code feels sequential, and it’s quite easy to understand the flow of events ; it’s very explicit yet you never have to run the callbacks yourself, the exceptions do show up, and you don’t even need to manipulate a `loop` object anymore! If you're trying to learn how to use it, my advice would be:
* "Stick to the official documentation[1]!". Many resources found online are outdated, and give convoluted or plain wrong examples, and fail to mention the recent additions.
* Use `asyncio.run`. The alternative way (using get_event_loop() and loop.run_until_complete() is cumbersome and hard to get right. Even the documentation wasn't correct[2].). The part on Coroutines and Tasks is well-written, and the best part is
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the examples. Simply reading all the examples on after another gives a a good insight on how asyncio should be used.
* If you want to work with sockets, use the high-level "Streams"[3] if you want to stay in the standard library. `asyncio.start_server` is a powerful abstraction. If you’re willing to use a third-party library, I found that `pynng`[4] was a breeze to work with. It is compatible with asyncio and other async frameworks, and it found it more straightforward than pyzmq, which is also compatible with asyncio[5].
* If you want to run async functions in the main event loop and blocking functions in threads (with `loop.run_in_executor), Janus[7] seems to be a great way to share data. I have not used it yet though.
My use case was that I wanted to read sensor data on one computer (server) and broadcast it to other computers (clients) which would in turn graph it live, or write it to disk. The server used `pyserial_asyncio`[6] to asynchronously read serial data and published it via TCP using a the pub/sub scheme from pynng (pynng.Pub0).
The clients could then either synchronously or asynchronously receive the data by subscribing to the server (pynng.Sub0), and make plots in realtime.
[1]: https://docs.python.org/3/library/asyncio.html
[2]: https://github.com/python/asyncio/pull/465#issue-93620963
[3]: https://docs.python.org/3/library/asyncio-stream.html#asynci...
[4]: https://pypi.org/project/pynng/
[5]: https://pyzmq.readthedocs.io/en/latest/api/zmq.asyncio.html
[6]: https://github.com/pyserial/pyserial-asyncio
[7]: https://github.com/aio-libs/janus