Typing docs: increase prominence of warnings regarding @runtime_checkable
#127985
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
AlexWaygood
added
skip issue
skip news
topic-typing
needs backport to 3.12
JukkaL
reviewed
Dec 16, 2024
|
|
||
| Runtime-checkable protocols are known to be unsafe in several ways. | ||
| Runtime-checkable protocols are known to be unsound in several ways. | ||
| You should only use them for simple protocols, and even then only use |
There was a problem hiding this comment.
What about suggesting that they should only be used for method-only protocols? Or just for protocols with dunder methods -- since dunder methods typically have a well-understood signature, so the check is more likely to do the right thing at runtime?
There was a problem hiding this comment.
It isn't safe on even just dunder methods. An example of this is numpy arrays and __bool__, see other discussion about type checkers making unsafe assumptions related to this here
JelleZijlstra
approved these changes
Mar 3, 2025
|
@AlexWaygood this has a conflict now, and some suggested wording changes. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
6 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
We have some warnings in the docs for
typing.runtime_checkablealready, but:This PR makes the warnings more prominent and expands on the examples. It follows renewed discussion on how runtime-checkable protocols are fundamentally unsafe in many ways on the Discourse thread https://discuss.python.org/t/pep-767-annotating-read-only-attributes/73408
📚 Documentation preview 📚: https://cpython-previews--127985.org.readthedocs.build/