ENH: Add ctype aliases for numeric types of specific sizes to Python

[N-Dekker]

Added the following aliases:

float32_ctype
float64_ctype
uint8_ctype
uint16_ctype
uint32_ctype
uint64_ctype
int8_ctype
int16_ctype
int32_ctype
int64_ctype

Aims to provide a more human-readable alternative to F, D, UC, US, UI, ULL, SC, SS, SI, and SLL. Eases writing code for which the specific size of numeric types should be platform-independent.

Typical use cases, specifying the pixel type of an image:

• itk.Image[itk.uint8_ctype, 2] (equivalent to itk.Image[itk.UC, 2])
• itk.Image[itk.float64_ctype, 2] (equivalent to itk.Image[itk.D, 2])

[greptile-apps]

Greptile Summary

This change adds top-level Python aliases for fixed-width integer and floating-point ITK C types, with regression coverage registered for their NumPy dtype mappings.

Confidence Score: 5/5

No blocking failure remains.

No accepted blocking findings remain.

T-Rex Logs

What T-Rex did

• The team attempted the documented Pixi build command and observed it could not progress because the Pixi package manager was not installed.
• The team attempted the registered focused test with the build-tree using PYTHONPATH and observed a ModuleNotFoundError for itk, indicating that ITK Python is not built or installed in the environment.
• The blockers were captured and a path forward was outlined: install Pixi, build the declared Python 3.13 ITK wrapper environment, then re-run the build commands and the ctest suite.

_{Ran code and verified through T-Rex}

_{Reviews (2): Last reviewed commit: "ENH: Add ctype aliases for numeric types..." | Re-trigger Greptile}

[thewtex]

How about using uint8, etc per:

https://github.com/InsightSoftwareConsortium/ITK/blob/main/Wrapping/Generators/Python/itk/support/extras.py#L266-L295

?

[N-Dekker]

How about using uint8, etc per:
https://github.com/InsightSoftwareConsortium/ITK/blob/main/Wrapping/Generators/Python/itk/support/extras.py#L266-L295
?

Thanks Matt, can you please elaborate a little bit? For example, how would you define a 2D itk Image of int64 pixels? With the proposed PR, it would be itk.Image[itk.int64_ctype, 2].

---

P.S. It looks like there is a bug at

ITK/Wrapping/Generators/Python/itk/support/extras.py

Line 286 in d56ecc0

np.dtype(np.int64): itk.SL,

    # This is a Mapping from numpy array types to itk pixel types. (Bug?)
    _np_itk = {
        ...
        np.dtype(np.int64): itk.SL,
        ...
     }

itk.SL is not int64, on Windows. Once this pull request is merged, it can be fixed by doing:

    # This is a Mapping from numpy array types to itk pixel types. (Fixed!)
    _np_itk = {
        ...
        np.dtype(np.int64): itk.int64_ctype,
        ...
     }

Is that what you meant to say?

[thewtex]

itk.Image[itk.int64_ctype, 2].

I think it would be easier to write, easier to read, and more expected names if we had itk.Image[itk.int64, 2] or itk.Image[np.int64, 2].

np.dtype(np.int64): itk.SL,

Good catch!

[N-Dekker]

Update: Inspired by Matt's comments, I just renamed the proposed aliases (with this force-pushed amend) to:

float32_t
float64_t
uint8_t
uint16_t
uint32_t
uint64_t
int8_t
int16_t
int32_t
int64_t

Under the hood, they are still simply aliases of itk.F, itk.D, itk.UC, etc.

The PR will now allow users to write (for example) itk.Image[itk.int64_t, 2], which looks very similar to the C++ equivalent, itk::Image<std::int64_t, 2>.

Hope that it's good enough now!