Make BaseDescriptor generic wrt the owning class#254
Merged
Conversation
Previously, BaseDescriptor typed the owning object as `Thing`, which was a bit loose and led to some vague type hints (particularly for functional properties and actions). I've added a second generic parameter for the owning class. This makes some of the type test code a bit more verbose, but it gets rid of a fair few `type: ignore` statements and also means we now detect a few type errors that were previously missed. This is mostly tidying up, but will be useful for some PRs in the near future.
This uses the new generic parameter for the descriptor's Owner to correctly type the function's `self` parameter, among other things.
This was a one-character fix: we now need the second argument when inspecting `__orig_class__` to get the value type. This is only used when a descriptor is created using subscript syntax, e.g. `prop = Property[Thing, int](default=0)`. Happily, it was picked up in tests, and is now passing.
This now correctly uses the `Owner` type variable in `BaseDescriptor`. `mypy` picked up an inconsistency between this and `ActionDescriptor`, but oddly not on Python 3.10.
julianstirling
approved these changes
Feb 2, 2026
Contributor
julianstirling
left a comment
julianstirling
left a comment
There was a problem hiding this comment.
One thing I am confused about that could do with a comment. Otherwise this seem like a significant improvement in type specificity.
rwb27
force-pushed
the
generic-owner-for-descriptors
branch
from
4979167 to
93dd2dc
Compare
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
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
Previously, BaseDescriptor typed the owning object as
Thing, which was a bit loose and led to some vague type hints (particularly for functional properties and actions).I've added a second generic parameter for the owning class. This makes some of the type test code a bit more verbose, but it gets rid of a fair few
type: ignorestatements and also means we now detect a few type errors that were previously missed.This is mostly tidying up, but will be useful for some PRs in the near future.
Closes #217
Closes #162