Not clear why HTML rendering needed to be infected with async. None of the example code has a clear need for async - even the `is_admin()` method would be a prefetched property in any reasonable database model.
Async infrastructure allows your stuff to be sync or async. While sync infrastructure forces your stuff to be sync.
If anything sync (not async) infects everything you do.
Of course it depends if you call the infrastructure (then it's better for it to be sync) of if the infrastructure calls you (then it's better to be async).
Rendering engine is something you rarely call, but it often calls your functions.
Yes, and that’s the worst part of async. That’s why you need to be very strategic about where you introduce it into your code in order to minimize the number of functions it infects, not give up and write a framework that’s all async for no good reason.
https://journal.stuffwithstuff.com/2015/02/01/what-color-is-...
Yes. But you should be equally strategic about introducing sync code into your platform. Because making your platform sync basically makes it only be able to call sync functions of your code.
It's not that async infects. It's sync that infects and restricts. We are just used to it by default.
The fact that we started from sync was the cause of all the trouble of rpc because everything outside of CPU is innately async.
So make your utility functions sync whenever you can but make your platforms and frameworks async.
I just completely disagree. Async is syntactic sugar that can be reduced to sync code with callbacks. It doesn’t exist on equal footing. If you want to call sync code from async code, you just… call it. If it performs blocking IO, it’ll block, but that’s exactly what it would do if called from other sync code, too.
By contrast, calling async code from sync code requires a special blocking wrapper (Python) or unavoidably breaks control flow (JavaScript).
> Async is syntactic sugar that can be reduced to sync code with callbacks
The whole point of introducing async was to get away from callback hell.
> By contrast, calling async code from sync code requires a special blocking wrapper (Python) ...
That's exaclty my point. If you don't have async by default in your platform you need to do stupid things to fake it. If function calls and main in Python were innately async you could be calling async code just as easily as sync code.
> [...] or unavoidably breaks control flow (JavaScript).
async/await syntax avoids it completely.
Tbh await should be default function call semantics and there should be special keyword for calling without awaiting. But since we come from sync primitives that would require small revolution that might happen at some point.
> Async is syntactic sugar
You could make sync code be syntactic sugar for await.
> would require small revolution that might happen at some point.
or python could have blessed gevent and done away with all the nonsense.
I hope that someone does an oral history of why gevent wasn't seen as the solution here. The existence of models like Twisted, and a general idea that yields to an event thread should be explicit in some way, I think caused the exact kind of fracturing of the ecosystem that everyone was trying to avoid. "Everyone will write async code" simply didn't happen in practice.
> Async infrastructure allows your stuff to be sync or async. While sync infrastructure forces your stuff to be sync.
Is that specific to the threading model for Python?
The reverse is true in nodejs where once you’ve got one async call, the entire chain must be async.
Python is the same as JS.
Async function (that returns something you need) can be called only from async function. That's why autor of this specific rendering framework/lib chose it to be async. So that the user functions called in components can be either sync or async.
Thanks for this answer. Async support is handy if the framework in which you're using the tools is async (let's say FastAPI). See my answer to a similar question on reddit: https://www.reddit.com/r/Python/comments/1fvv11p/comment/lqb...
Your counterpoint still naturally involves something like async _somewhere_ (your proposal is just to move it out of the HTML rendering and into an initial data-gathering stage). If you accept that premise then the question is just where the async code goes.
While on some level it makes sense for HTML rendering to be a pure function where the inputs are gathered from elsewhere (potentially asynchronously), it looks like htmy wants to make it easy to define hierarchies of components. Instead of `is_admin()`, imagine a dashboard whose layout is stored in a database, supporting configurable charts of various flavors. The heterogeneity of the data supporting different types of charts makes it hard to efficiently pull data in a single SQL query (equivalently, any reasonable database model), so somewhere in your code you're pulling a bunch of data asynchronously, and somewhere else you're rendering it. The question, still, is "where?"
Going back to the idea of htmy defining hierarchies of components, imagine how annoying it would be to have to manually grab all the data for a "reporting page" component only to feed it straight back into the renderer -- either having to duplicate the hierarchial structure when feeding data into the renderer (a technique some UI libraries employ, though I don't like it) -- or having to come up with a method for flattening that hierarchy when instantiating the component (another technique some UI libraries employ, one I like more for small projects and less for large ones).
They solve that (to the extent that you think it needs solving) by bundling all that background logic into the components themselves. Did they really need to implement that recursively instead of just walking the hierarchy, gathering the data up-front, and populating it? Eh. The code winds up being similar either way, and either way it definitely forces async back into the middle of HTML rendering.
Mind you, that tends to either make some applications hard to build or to cause the framework to explode in complexity over time as people need new and new ways to say "yes, re-render this thing; no, re-render that other thing, but don't grab its data, ...." There's enough less particularly annoying code involved though that fat, smart components are a natural place for people to gravitate.
Unrelated to htmy completely, a technique I like from time to time even for problems which don't need async per se (and I'm usually using lower-level languages, so the implementation is some sort of more manual continuation pattern, but all those things are basically async, so I won't dwell on the details) is explicitly designing pausable/restartable structures for long-running computations. It's about as easy to write as purely iterative code, and you can run the result as purely iterative with no runtime overhead, so the downsides are low. It opens the door though to easily tuning how long you defer invariant maintenance (too infrequent and your algorithm devolves to the slow thing it's replacing, too frequent and the overhead isn't worth it), easily checkpointing a computation, adding other custom runners for an algorithm (like animating its progress), .... I can absolutely see a use-case for wanting to visualize each step of an HTML rendering, or log OS network counters after each step, and so on. Python's async isn't really the right tool for the job for that (it's hard to modify the runtime to support them without building quite a lot of nonsense from scratch), but async in the abstract isn't bad at all per se.
Imagine you have 2 big components, one fetches from an third-party API and the other from your backend, this way they can load at the same time instead of sequentially.
I was imagining more like you have a Django view that does all the async data fetching and then you hand off the results to a 'dumb' page component that does only rendering
I guess the point is to have components know how to fetch their own data, particularly when combining with HTMX and having backend return page fragments that correspond to components. But maybe this makes more sense in React than it does when translating the pattern back to server-side?
e.g. same author has this https://github.com/volfpeter/fasthx?tab=readme-ov-file#htmy-... which is doing that, but there's still a 'view' endpoint. Why not put the data fetch code there and have 'dumb' components that don't need to be async?
You're right, fetching all the data (that you may or may not need during rendering) in advance is of course doable and quite common. That's what you do for example with tools like Jinja. That may or may not work well for your use-case.
htmy does not force you to put data fetching or anything else into components (you can still have dumb components). It also doesn't force you to write async components. The most important thing it does is it gives you the option to build your application entirely in Python (no ugly custom templating language syntax with lack of static analysis or proper IDE support) and enables the use of modern async tools.
And admittedly, the lib was built with FastAPI and HTMX in mind, which kind of necessitates async support...
My comment was just thinking out loud really...
It seems like if you're not doing data fetching in the component then there's no need for it to be async.
And then I was wondering if maybe data fetching in components was a good pattern. It's quite different from what I'm used to doing.
It seems like the view endpoint would be for functionality shared the full view, like auth safeguards and such, while the components would fetch the data they need; this would make it so you don't need to pass around the data to the view and save a few lines of code; of course this is not compatible with the idea of having "dumb" components vs "logic" ones like people do in React and alike.
Components don't really need to fetch anything, they don't need to be smart. It's up to you where data fetching happens. If you look at fasthx for example, you'll see that routes/views normally handle your business logic and fasthx does the rendering (now with Jinja or htmy). With Jinja for example, it can only work like this. With htmy, you have more flexibility (which can be an advantage but of course it can also be misused).
Async components can be handy for example when you need to load files. See the Snippet utility and the markdown support in the lib. https://volfpeter.github.io/htmy/examples/markdown/
Because checking for two conditions is impossible? This seems like a solution for a non-existent problem. I could be missing something
But does it actually work that way? If I `await fetch_from_api()` in the first component before returning the tree with the second component that fetches from my backend, `fetch_from_api()` has to resolve before Htmy finds out about the second component.