Szorc: Mercurial's Journey to and Reflections on Python 3

Posted Jan 20, 2020 22:44 UTC (Mon) by HelloWorld (guest, #56129)
In reply to: Szorc: Mercurial's Journey to and Reflections on Python 3 by smurf
Parent article: Szorc: Mercurial's Journey to and Reflections on Python 3

Python doesn't have a problem with resources to be closed (that's what "with foo() as bar"-style context managers are for), nor concurrency (assuming that you use Trio or anyio).

Sure, you can solve every problem that arises from adding magic features to the language by adding yet more magic. First, they added exceptions. But that interacted poorly with resource cleanup, so they added with to fix that. Then they realized that this fix interacts poorly with asynchronous code, and they added async with to cope with that. So yes, you can do it that way, because given enough thrust, pigs fly just fine. But you have yet to demonstrate a single advantage that comes from doing so.

On the other hand, there are trivial things that can't be done with with. For instance, if you want to acquire two resources, do stuff and then release them, you can just nest two with statements. But what if you want to acquire one resource for each element in a list? You can't, because that would require you to nest with statements as many times as there are elements in the list. In Scala with a decent library (ZIO or cats-effect), resources are a Monad, and lists have a traverse method that works with ALL monads, including the one for resources and the one for asynchronous tasks. But while asyncio.gather (which is basically the traverse equivalent for asynchronous code) does exist, there's no such thing in contextlib, which proves my point exactly: you end up with code that is constrained to specific use cases when it could be generic and thus much easier to learn because it works the same for _all_ monads.

Szorc: Mercurial's Journey to and Reflections on Python 3

Posted Jan 21, 2020 6:51 UTC (Tue) by smurf (subscriber, #17840) [Link] (1 responses)

> But what if you want to acquire one resource for each element in a list?

You use an [Async]ExitStack. It's even in contextlib.

Yes, functional languages with Monads and all that stuff in them are super cool. No question. They're also super hard to learn compared to, say, Python.

Szorc: Mercurial's Journey to and Reflections on Python 3

Posted Jan 21, 2020 14:32 UTC (Tue) by HelloWorld (guest, #56129) [Link]

> You use an [Async]ExitStack. It's even in contextlib.
You can *always* write more code to fix any problem. That isn't the issue here, it's about code reuse. ExitStack shouldn't be needed, and neither should AsyncExitStack. These aren't solutions but symptoms.

> They're also super hard to learn compared to, say, Python.
For the first time, you're actually making an argument for putting the things in the language. But I'm not buying it, because I see how much more stuff I need to learn about in Python that just isn't necessary in fp. There's no ExitStack or AsyncExitStack in ZIO. There's no `with` statement. There's no try/except/finally, there's no ternary operator, no async/await, no assignment expressions, none of that nonsense. It's all just functions and equational reasoning. And equational reasoning is awesome _because_ it is so simple that we can teach it to high school students.