this post was submitted on 15 Nov 2023
25 points (87.9% liked)

Python

6375 readers
4 users here now

Welcome to the Python community on the programming.dev Lemmy instance!

πŸ“… Events

PastNovember 2023

October 2023

July 2023

August 2023

September 2023

🐍 Python project:
πŸ’“ Python Community:
✨ Python Ecosystem:
🌌 Fediverse
Communities
Projects
Feeds

founded 1 year ago
MODERATORS
 

This is a discussion on Python's forums about adding something akin to a throws keyword in python.

you are viewing a single comment's thread
view the rest of the comments
[–] palebluethought@lemmy.world 10 points 1 year ago (2 children)

Aren't checked exceptions in Java generally regarded as a bad mistake?

[–] Nevoic@lemm.ee 9 points 1 year ago

Yes, but not because the goal of having exceptions in types is bad, rather Java's type system isn't advanced enough to support the ideal solution here.

Scala 3 is working on experimental capture checking capabilities, which allows functions to express certain capabilities (file access, networking, db, etc.), and CanThrow capabilities (e.g exceptions at the type level) are one reification of this.

The CanThrow docs I linked have a good introduction into why Java checked exceptions are bad, and how Scala's alternative is far better. Essentially it comes down to a lack of polymorphism in checked exceptions. In practice this means they're incredibly verbose outside of simple usecases, and with a very easy escape hatch (RuntimeException), you don't even get the guarantee of knowing a function without checked exceptions doesn't throw.

Python will also have this latter issue. Python's "typing" in general has this issue actually. Types aren't validated unless you use an external tool, and even then Any is a leaky abstraction that can hide any level of typing errors, unlike in properly typed languages where it's not leaky. You need it to be leaky in gradually typed environments, or you wouldn't be able to use a ton of the Python ecosystem, but this vastly reduces the effectiveness of the typing solution.

I don't know if Python's solution here will address the lack of polymorphism that Java's solution has, I'll have to look into it more.

[–] SittingWave@programming.dev 3 points 1 year ago (1 children)

I heard the same, but not sure why. Do you have a link?