Add typing and collections.abc module prefix

[gentlegiantJGC]

Description

Add typing. and collections.abc prefix to remove ambiguity.

Suggested changelog entry:

Fix typing and collections.abc type hint ambiguity.

[gentlegiantJGC]

The tests need updating to reflect these changes.
Please give an indication if this is something you would consider merging and I will update the tests.

[henryiii]

@InvincibleRMC, thoughts?

[InvincibleRMC]

I think this is a good idea. This was discussed a little in and around #5566 (comment). Adding the module prefix will allow users to create their own Sequence class for example and not have the type hints conflict with typing.Sequence see issues like sizmailov/pybind11-stubgen#241.

[rwgk]

Looks good to me, but do we actually still want to support Python 3.8?

Python 3.8 EOL was 2024-10-07

[rwgk]

Suggestion to make these

PYBIND11_TYPE_HINT_...

so they line up nicely and are easier to pin-point.

[rwgk]

// Python 3.9+ Compatibility

?
(The + is the most important aspect of my suggestion.)

[gentlegiantJGC]

do we actually still want to support Python 3.8?

You still have test runners for 3.8 so I assumed you still supported it.
I couldn't find anything saying what your minimum supported version was.
If you want to drop support then it would simplify this.

[rwgk]

If you want to drop support then it would simplify this.

Me: yes

But I'll go with @henryiii's judgement.

[henryiii]

Let's keep it for 3.0. We can drop it for 3.1.

[henryiii]

I couldn't find anything saying what your minimum supported version was.

It's in setup.cfg (or pyproject.toml after #5598)

[gentlegiantJGC]

I think I am going to scale back this pull request to just adding the module prefix.
Fixing the issue in 3.8 is going to require a lot of changes to the tests which seems pointless for a version that has reached end of life.
I will leave the 3.8 macros but commented out so someone can add them later if they want.

[gentlegiantJGC]

I have fixed the tests.
This only includes adding the module prefixes for typing and collections.abc.
I have no personal interest in supporting Python 3.8 so I will leave that to someone else.
I have left the type hint macros for 3.8 in common.h but commented out to make it easier if someone does want to fix the 3.8 issues. This should just be a case of uncommenting the macros and updating the tests with a switch based on python version.

[henryiii]

If you want it to go into 3.0, 3.8 needs to work (where "work" is very loosely defined as "not be worse that it is now"). If you are fine to wait till after 3.0 (like a week), then no need to worry about 3.8. I'd personally go for the latter.

[gentlegiantJGC]

This can wait for 3.1. I have removed the 3.8 compatibility macros and moved the strings inline.

[gentlegiantJGC]

I don't know why that test is failing

[rwgk]

All tests pass.

@gentlegiantJGC do you want to merge this now (looks good to me)? Or wait until after the v3.0.0 release?

[gentlegiantJGC]

This can't be merged yet because it changes the following which are incompatible with Python 3.8
(typing.)Iterable -> collections.abc.Iterable
(typing.)Iterator -> collections.abc.Iterator
(typing.)Callable -> collections.abc.Callable
(typing.)Sequence -> collections.abc.Sequence

I decided not to support 3.8 because it would make the codebase more complex for something which is getting removed which felt pointless.

[rwgk]

I decided not to support 3.8 because it would make the codebase more complex for something which is getting removed which felt pointless.

Sounds good. I'm just curious: What exactly is incompatible? Certain type checkers when running under 3.8? We're not testing that here? Could/should we?

[henryiii]

Aren't these strings? Those are valid at type-check time, just not turning them into non-string annotations at runtime. I think that's not terrible, though? We might even have examples elsewhere? Our annotations are very much not runnable at runtime already.

[gentlegiantJGC]

You are correct that this changes nothing about the runtime behaviour.
It only changes the type hints that pybind11 embeds in the docstrings that can be used to generate stub files which static type checkers can use.

The collections.abc variants were added in 3.9 so a static type checker would correctly error that they don't exist.
That being said typing.h currently uses tuple[], dict[], list[] and set[] which were not subscriptable in Python 3.8 so static type checking in 3.8 is already broken if any of those are used. This behaviour was also implemented in 3.9.

[gentlegiantJGC]

We're not testing that here? Could/should we?

It probably wouldn't hurt. You can use pybind11-stubgen to generate stubs for your test suite and then run mypy on the result.

It would catch issues like this in the future.

[henryiii]

Type checkers shouldn't care if a .pyi file is not runnable. Just like they don't care about from __future__ import annotations, or if you put the string "list[int]" into a type annotation. Runtime cares, but runtime can't access a .pyi file anyway.

Generally for type hints, if new syntax ([] or |, for example) gets added, type hints can update to it unless they are runtime evaluated (which the default in <3.14, but strings, future, and pyi are not).

[gentlegiantJGC]

Upon further research it seems that mypy has backported class subcription and collection.abc classes to 3.7 so I see no issue merging this now. I assumed they would use the functionality of that version.

I still think it is worth validating the generated type hints. It would have caught issues like #5662 which did raise errors in mypy in older versions.

# type_check.pyi
from __future__ import annotations

from collections.abc import Buffer

def return_buffer() -> Buffer: ...

# mypy -m type_check
type_check.pyi:3: error: Module "collections.abc" has no attribute "Buffer"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)

[timohl]

Good change (also thanks for the typing.Buffer PR 👍).

This can't be merged yet because it changes the following which are incompatible with Python 3.8 (typing.)Iterable -> collections.abc.Iterable (typing.)Iterator -> collections.abc.Iterator (typing.)Callable -> collections.abc.Callable (typing.)Sequence -> collections.abc.Sequence

I decided not to support 3.8 because it would make the codebase more complex for something which is getting removed which felt pointless.

If using the collections.abc.* variants over typing.* creates problems with type checkers in Python 3.8, you could still use the typing.* variants here and when 3.8 is dropped, it could be switched to collections.abc.* (should be a simple search and replace).
Well, IF pybind should have correct type hints for 3.8.

Looking over the current state of type hints:

• typing.Annotated is also a candidate that breaks 3.8 type checking right now (was added in 3.9).
• types.CapsuleType was added in 3.13, maybe this should be handled similar to typing.Buffer?

In my opinion, pybind v3 should support correct type hints for 3.9+.
Previously, type hints were broken in several places for all Python versions anyway.
If support for 3.8 (which officially reached end-of-life in October 2024) is going to be dropped anyway, type hints might as well stay partially broken until then (unless somebody finds this important and wants to put in the work).

For 3.9+ type hints, we could also think about replacing typing.Union[X, Y] with X | Y and typing.Optional[X] with X | None.
Not an important change but makes things more compact and "Using that [Union] shorthand is recommended." (Python docs)