Fetch type name dynamically on cast errors instead of using `PyTypeInfo::NAME` #5387

Tpt · 2025-09-01T16:16:59Z

Introduce PyTypeCheck::classinfo_object that returns an object compatible with instance and make use of it.
Remove PyTypeCheck::NAME

codspeed-hq · 2025-09-01T16:31:17Z

CodSpeed Performance Report

Merging #5387 will degrade performances by 10.84%

_{Comparing Tpt:tpt/dynamic-type (01d11e1) with main (6a6ed99)}

🎉 Hooray! `codspeed-rust` just leveled up to 3.0.5!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

❌ 1 regression
✅ 99 untouched

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	`BASE`	`HEAD`	Change
❌	`vec_bytes_from_py_bytearray_small`	770 ns	863.6 ns	-10.84%

davidhewitt

Thanks for moving this forward. I wonder if we should be concerned by the performance hit? It's not surprising as we're moving work from compile-time to runtime, at the benefit of better accuracy. I wonder if there are ways we can have our cake and eat it too? 🤔

src/instance.rs

davidhewitt

Thanks, looks very promising! I think there might be a couple other locations to change (see other comment)

... this might lead to some error messages changing in tests.

davidhewitt · 2025-09-02T14:01:44Z

src/instance.rs

I think there are other callsites to change in this file

cast and cast_into

Borrowed::cast

Sadly it won't work because they use the PyTypeCheck trait and not the PyTypeInfo trait

I had a quick look at the types implementing PyTypeCheck and not PyTypeInfo. It's

datetime types when abi3 is enabled. This can be fixed easily: DateTime: implement PytypeInfo even using the stable ABI #5388

protocol-like types (PyCode, PyIterator, PyMapping, PySequence, PyWeakref, PyWeakrefProxy and PyWeakrefReference). My guess is that we might implement PyTypeInfo on them, returning the collections.abs or similar types in type_object_raw impl and using the fast C method in is_type_of

What do you think about it?

Aside: rust-numpy does not implement PyTypeCheck explicitly.

#5402 #5403 #5404 remove all explicit implementations of PyTypeCheck except the ones on PyWeakrefProxy and PyWeakref. Both of them do not have immediate Python equivalents at my knowledge

Added PyTypeCheck::classinfo_object that provides a workaround

Tpt · 2025-09-05T08:24:47Z

src/err/mod.rs

 impl<'a, 'py> DowncastError<'a, 'py> {
    /// Create a new `PyDowncastError` representing a failure to convert the object
    /// `from` into the type named in `to`.
    pub fn new(from: &'a Bound<'py, PyAny>, to: impl Into<Cow<'static, str>>) -> Self {


DowncastError::new and DowncastIntoError::new are unused now. Do we want to replace the second parameter with a Bound<'py, PyAny>?

I think we should leave this for the moment, as public API. We might want to re-name / re-introduce this as CastError, and if so, we could "fix" the API and deprecate this one at the same time.

davidhewitt

Thanks, this is looking great, the improved error messages make me very happy! I think let's just make this land slightly softer for users with a deprecation, I don't think we need the immediate removal.

davidhewitt · 2025-09-07T20:13:12Z

src/type_object.rs

-    /// Name of self. This is used in error messages, for example.
-    const NAME: &'static str;


Can we make this #[deprecated] instead of removing? The deprecation message can recommend users get a "name" at runtime from classinfo_object, perhaps.

(We might be able to default it to empty, so that users don't need to implement it, we might want to leave existing implementations in PyO3 for a couple of versions just in case users are depending on it.)

Done in 6a9135f. This is indeed used by a few repos on GitHub. I added a longer deprecation message because most of them are doing their own version of cast.

Tpt · 2025-09-08T07:27:34Z

With this MR all remaining usages of PyTypeInfo::NAME and PyTypeInfo::MODULE are bounded by PyClass.

davidhewitt

Fantastic, thank you!

Tpt · 2025-09-15T08:57:15Z

@davidhewitt Thank you! f5fbe62 should fix the CI (the type name is different in 3.9)

Tpt · 2025-09-22T10:09:32Z

Rebase done: 1963b29

# Conflicts: # src/types/sequence.rs

Tpt force-pushed the tpt/dynamic-type branch from c459414 to 7b921c9 Compare September 2, 2025 07:53

Tpt marked this pull request as ready for review September 2, 2025 07:53

davidhewitt reviewed Sep 2, 2025

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davidhewitt mentioned this pull request Sep 3, 2025

PyIterator, PyMapping, PySequence: implement PyTypeInfo #5402

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Tpt mentioned this pull request Sep 4, 2025

implement PyTypeInfo on PyWeakref and PyWeakrefProxy #5409

Closed

Tpt force-pushed the tpt/dynamic-type branch from ce7a0f6 to 196ed31 Compare September 5, 2025 08:21

Tpt commented Sep 5, 2025

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Tpt force-pushed the tpt/dynamic-type branch 2 times, most recently from 062a32f to dd0d5c5 Compare September 5, 2025 09:11

davidhewitt reviewed Sep 7, 2025

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davidhewitt approved these changes Sep 14, 2025

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davidhewitt added this pull request to the merge queue Sep 14, 2025

davidhewitt mentioned this pull request Sep 14, 2025

fill PyTypeInfo::NAME with Pythonic values (e.g. BaseException) instead of C ones (e.g. PyBaseException) #5352

Open

github-merge-queue bot removed this pull request from the merge queue due to failed status checks Sep 14, 2025

Tpt added 6 commits September 15, 2025 10:52

Fetch type name dynamically on cast errors

6be2b86

Lazily fetch type name

48fee14

Derive Debug

755fa43

Introduce PyTypeCheck::classinfo_object and make use of it

f76455c

Add back PyTypeCheck::NAME

e0c8304

Fixes Python 3.9 tests

f5fbe62

Tpt force-pushed the tpt/dynamic-type branch from 6a9135f to f5fbe62 Compare September 15, 2025 08:56

davidhewitt enabled auto-merge September 15, 2025 08:58

auto-merge was automatically disabled September 22, 2025 10:09
Head branch was pushed to by a user without write access

Merge branch 'main' into tpt/dynamic-type

01d11e1

# Conflicts: # src/types/sequence.rs

Tpt force-pushed the tpt/dynamic-type branch from 1963b29 to 01d11e1 Compare September 22, 2025 16:53

davidhewitt added this pull request to the merge queue Sep 27, 2025

davidhewitt mentioned this pull request Sep 27, 2025

rename DowncastError into CastError #5393

Open

Merged via the queue into PyO3:main with commit 28db16c Sep 27, 2025
40 of 43 checks passed

davidhewitt mentioned this pull request Sep 27, 2025

deprecate downcast functions in favour of cast functions #5472

Open

		/// Name of self. This is used in error messages, for example.
		const NAME: &'static str;

Fetch type name dynamically on cast errors instead of using PyTypeInfo::NAME #5387

Fetch type name dynamically on cast errors instead of using PyTypeInfo::NAME #5387

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Merging #5387 will degrade performances by 10.84%

🎉 Hooray! codspeed-rust just leveled up to 3.0.5!

Summary

Benchmarks breakdown

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Tpt commented Sep 15, 2025

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Fetch type name dynamically on cast errors instead of using `PyTypeInfo::NAME` #5387

Fetch type name dynamically on cast errors instead of using `PyTypeInfo::NAME` #5387

Tpt commented Sep 1, 2025 •

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🎉 Hooray! `codspeed-rust` just leveled up to 3.0.5!

Tpt Sep 2, 2025 •

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