Support Python dispatching on PrimaryInputName

[thewtex]

We should dispatch on PrimaryInputName when it is passed as a keyword argument instead of a positional parameter.

xref:

• https://github.com/SuperElastix/elastix/blob/368d71649c9052b47396b9eb7c0069fa7ea24b7f/Core/Main/itkElastixRegistrationMethod.hxx#L55
• Error when using keyword arguments for the itk.elastix_registration_method ITKElastix#212

CC: @N-Dekker @mstaring

[N-Dekker]

@thewtex I'm glad you are looking at this issue. Is the following supposed to work well?

    output_image = itk.median_image_filter(input=my_float_image)

(It now says TypeError: Expecting argument of type itkImageSS2 or itkImageSourceISS2). Or should the keyword argument start with a capital, Input=my_float_image? I'm asking, because "Input" is in the list of so-called primary_input_methods at:

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

Line 672 in 15af3ae

primary_input_methods = ("Input", "InputImage", "Input1")

And primary_input_methods is used for dispatching:

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

Lines 711 to 716 in 15af3ae

	elif set(primary_input_methods).intersection(kwargs.keys()):
	for method in primary_input_methods:
	if method in kwargs:
	input_type = output(kwargs[method]).__class__
	keys = ttype_for_input_type(keys, input_type)
	break

Regarding ITKElastix issue InsightSoftwareConsortium/ITKElastix#212, obviously, "FixedImage" and "MovingImage" are not in primary_input_methods (and neither are "fixed_image" and "moving_image"). So I guess primary_input_methods should be extended, right?

[blowekamp]

The Process object maintains a lists of index inputs and named inputs. And a named input can be marked as primary. These named inputs are already coded input many filters e.g.
PDEDeformableRegistrationFilter

The information in the Process object should likely be used.

[N-Dekker]

Thanks @blowekamp I see, PDEDeformableRegistrationFilter has inputs named "FixedImage" and "MovingImage":

ITK/Modules/Registration/PDEDeformable/include/itkPDEDeformableRegistrationFilter.hxx

Lines 42 to 46 in 15af3ae

	// #1 "FixedImage" required
	Self::AddRequiredInputName("FixedImage", 1);
	// #2 "MovingImage" required
	Self::AddRequiredInputName("MovingImage", 2);

So then, should something like the following work, for itk::Image<float> objects float_image1 and float_image2?

itk.pde_deformable_registration_filter(FixedImage=float_image1, MovingImage=float_image2)

(It now says TypeError: Expecting argument of type itkImageSS2 or itkImageSourceISS2)

[dzenanz]

In procedural interface, the parameters get converted to snake_case, so try this: itk.pde_deformable_registration_filter(fixed_image=float_image1, moving_image=float_image2).

[blowekamp]

I would expect ProcessObject::GetPrimaryInputName to be useful.

I am not too sure of these details in ITK Python. Specifically if the Process object's name inputs/outputs are used or if it's just mapping keyword arguments to methods.

Also I think that PDE deformable registration class may be a base class for the deacons methods, and I have a harder guess of which is the primary input, and how the template parameters get mapped from it.

[thewtex]

Is the following supposed to work well?

    output_image = itk.median_image_filter(input=my_float_image)

The keyword here to be supported would be the snake_case version of itk::MedianImageFilter::GetPrimaryInputName();

[thewtex]

Will be closed via #4921