5 ms·

No, determinstic scheduling is not a property of async python. Yes, the stdlib asyncio event loop does have deterministic scheduling, but that's an implementat

No, determinstic scheduling is not a property of async python. Yes, the stdlib asyncio event loop does have deterministic scheduling, but that's an implementation detail and I would not rely on it for anything critical. Other event loops - for instance trio [1] - explicitly randomize startup order so that you won't accidentally write code that relies on it. [1] https://github.com/python-trio/trio/issues/32 https://github.com/python-trio/trio/issues/32

KraftyOne 6mo ago
It's been a stable (and documented) behavior of the Python standard library for almost a decade now. It's possible it may change--nothing is ever set in stone--but that would be a large change in Python that would come with plenty of warning and time for adjustment.
- 9dev 6mo ago
  And then one day, Astral creates a new Python implementation in Rust or something that is way faster and all the rage, but does this particular thing different than CPython. Whoops, you can’t use that runtime, because you now have cursed parts in your codebase that produce nondeterministic behaviour you can’t really find a reason for.
  - ubercore 6mo ago
    That's a bit what it felt like when I was learning Rust async. I get it, but "ecosystems" of async runtimes have a pretty big cost.
  - stuartjohnson12 6mo ago
    and then all the serverless platforms will start using Astral's new rust-based runtime to reduce cold starts, and in theory it's identical, except half of packages now don't work and it's very hard to anticipate which ones will and will not and behold! You have achieved Deno
  - LtWorf 6mo ago
    If the python core team cared about not breaking things I wouldn't need to run my tests on all versions of python.
  - wavemode 6mo ago
    If I know anything about the Python community - that new runtime would simply never gain significant traction, due to the incompatibility.
- farsa 6mo ago
  Well, in my early days programming python I made a lot(!!) of code assuming non-concurrent execution, but some of that code will break in the future with GIL removal. Hopefully the Python devs keep these important changes as opt-ins.
StableAlkyne 6mo ago
> but that's an implementation detail That sounds familiar... https://stackoverflow.com/questions/39980323/are-dictionaries-ordered-in-python-3-6 https://stackoverflow.com/questions/39980323/are-dictionarie...
mort96 6mo ago
How do you differentiate between something that "happens to work due to an implementation detail" and a "proper feature that's specified to work" in a language without a specification?
- BrenBarn 6mo ago
  There's still documentation.
- nhumrich 6mo ago
  In a language without a spec? You don't. But python has a very strong spec.
  - mort96 6mo ago
    Where?
    - nhumrich 6mo ago
      peps.python.org
game_the0ry 6mo ago
I just realized how little I know about how async event loops.
OptionOfT 6mo ago
The good old Workflow XKCD matches this perfectly: https://xkcd.com/1172/ https://xkcd.com/1172/

KraftyOne 6mo ago

It's been a stable (and documented) behavior of the Python standard library for almost a decade now. It's possible it may change--nothing is ever set in stone--but that would be a large change in Python that would come with plenty of warning and time for adjustment.

9dev 6mo ago
And then one day, Astral creates a new Python implementation in Rust or something that is way faster and all the rage, but does this particular thing different than CPython. Whoops, you can’t use that runtime, because you now have cursed parts in your codebase that produce nondeterministic behaviour you can’t really find a reason for.
- ubercore 6mo ago
  That's a bit what it felt like when I was learning Rust async. I get it, but "ecosystems" of async runtimes have a pretty big cost.
- stuartjohnson12 6mo ago
  and then all the serverless platforms will start using Astral's new rust-based runtime to reduce cold starts, and in theory it's identical, except half of packages now don't work and it's very hard to anticipate which ones will and will not and behold! You have achieved Deno
- LtWorf 6mo ago
  If the python core team cared about not breaking things I wouldn't need to run my tests on all versions of python.
- wavemode 6mo ago
  If I know anything about the Python community - that new runtime would simply never gain significant traction, due to the incompatibility.
farsa 6mo ago
Well, in my early days programming python I made a lot(!!) of code assuming non-concurrent execution, but some of that code will break in the future with GIL removal. Hopefully the Python devs keep these important changes as opt-ins.

StableAlkyne 6mo ago

> but that's an implementation detail That sounds familiar... https://stackoverflow.com/questions/39980323/are-dictionaries-ordered-in-python-3-6 https://stackoverflow.com/questions/39980323/are-dictionarie...

mort96 6mo ago

How do you differentiate between something that "happens to work due to an implementation detail" and a "proper feature that's specified to work" in a language without a specification?

BrenBarn 6mo ago
There's still documentation.
nhumrich 6mo ago
In a language without a spec? You don't. But python has a very strong spec.
- mort96 6mo ago
  Where?
  - nhumrich 6mo ago
    peps.python.org

game_the0ry 6mo ago

I just realized how little I know about how async event loops.

OptionOfT 6mo ago

The good old Workflow XKCD matches this perfectly: https://xkcd.com/1172/ https://xkcd.com/1172/