Skip to content

Fix Python Scalar typing issue #27528 #27620

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom
Open
wants to merge 2 commits into
base: 4.x
Choose a base branch
from
Open

Fix Python Scalar typing issue #27528 #27620

wants to merge 2 commits into from
+66 −3

Conversation

killerdevildog
Copy link

  • Add ScalarInput and ScalarOutput types for better type safety
  • ScalarInput: Union[Sequence[float], float] for function parameters
  • ScalarOutput: Sequence[float] for function return values
  • Keep original Scalar type for backwards compatibility (deprecated)
  • Add refinement functions to apply new types to specific functions
  • Functions returning scalars now use ScalarOutput (mean, sumElems, trace)
  • Drawing functions now use ScalarInput for color parameters
  • Resolves MyPy compatibility issues with scalar return values
  • Maintains full backwards compatibility

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

  • I agree to contribute to the project under Apache 2 License.
  • To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
  • [x ] The PR is proposed to the proper branch
  • [x ] There is a reference to the original bug report and related work
  • There is accuracy test, performance test and test data in opencv_extra repository, if applicable
    Patch to opencv_extra has the same branch name.
  • [x ] The feature is well documented and sample code can be built with the project CMake

@asmorkalov asmorkalov requested a review from VadimLevin August 4, 2025 05:24
@asmorkalov asmorkalov added this to the 4.13.0 milestone Aug 4, 2025
@VadimLevin
Copy link
Contributor

Thank you for contribution.
I believe this approach is suboptimal, as it necessitates manual adjustments for each individual function.
The alternative is to generate function overloads that accept float argument and defining Scalar as:

AliasTypeNode.sequence_("Scalar", PrimitiveTypeNode.float_(),
                            doc="Max sequence length is at most 4"),

instead of

    AliasTypeNode.union_(
        "Scalar",
        items=(SequenceTypeNode("Scalar", PrimitiveTypeNode.float_()),
               PrimitiveTypeNode.float_()),
        doc="Max sequence length is at most 4"
    ),

Example:

@_typing.overload
def line(img: cv2.typing.MatLike, pt1: cv2.typing.Point, pt2: cv2.typing.Point, color: cv2.typing.Scalar, thickness: int = ..., lineType: int = ..., shift: int = ...) -> cv2.typing.MatLike: ...

# HERE GOES float OVERLOAD
@_typing.overload
def line(img: cv2.typing.MatLike, pt1: cv2.typing.Point, pt2: cv2.typing.Point, color: float, thickness: int = ..., lineType: int = ..., shift: int = ...) -> cv2.typing.MatLike: ...

@_typing.overload
def line(img: UMat, pt1: cv2.typing.Point, pt2: cv2.typing.Point, color: cv2.typing.Scalar, thickness: int = ..., lineType: int = ..., shift: int = ...) -> UMat: ...

# HERE GOES float OVERLOAD
@_typing.overload
def line(img: UMat, pt1: cv2.typing.Point, pt2: cv2.typing.Point, color: float, thickness: int = ..., lineType: int = ..., shift: int = ...) -> UMat: ...

Functions returning Scalar should be left as is

@_typing.overload
def mean(src: cv2.typing.MatLike, mask: cv2.typing.MatLike | None = ...) -> cv2.typing.Scalar: ...

@_typing.overload
def mean(src: UMat, mask: UMat | None = ...) -> cv2.typing.Scalar: ...

@killerdevildog
Fix Scalar typing issues using function overloads approach
f23ce03 
Addresses issues opencv#27528, opencv#26818, opencv#26826 by implementing the function
overloads solution suggested by VadimLevin in PR opencv#27620.

Changes:
1. predefined_types.py: Change Scalar from Union to Sequence[float]
2. api_refinement.py: Add global function overload generation
3. Generate both Scalar and float overloads for drawing functions

This provides better MyPy compatibility while maintaining backward
compatibility. All existing code continues to work unchanged.

Testing: Comprehensive test suite validates all scenarios pass
@killerdevildog killerdevildog force-pushed the fix-scalar-typing-issue-27528 branch from a9b79c8 to f23ce03 Compare August 12, 2025 06:46
@killerdevildog
Copy link
Author

@VadimLevin

FYI, I've rebased the branch and added a test, followed by a force push.
I'm still familiarizing myself with the codebase, github, and git so please be forgiving of any misunderstanding or sub optimal code submissions, and am eager to contribute. ( but please don't merge if its not up to par, most of these are learning experiences and trying to help with open source )
I reviewed the original issue #27528 which addressed issues #26818 and PR #26826 .
To accelerate my understanding, I consulted GitHub Copilot—please let me know if anything seems off!
I've built the code, and it compiled successfully. The test I added passed after a few iterations of failing.
If you have any further adjustments or feedback, please let me know! I tested it using a python venv, so I hope everything is good to go. let me know what you think.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Reviewers

@VadimLevin VadimLevin Awaiting requested review from VadimLevin

Assignees

@VadimLevin VadimLevin

Labels
category: python bindings
Projects
None yet
Milestone
4.13.0
Development

Successfully merging this pull request may close these issues.
3 participants
@killerdevildog @VadimLevin @asmorkalov