vtkDataObject subclassing example [python]

Support
1

I would like to pass customised data types into and out of a vtkAlgorithm subclass

Where can I find more python information about subclass vtkDataObject

The following is the gist of my idea of what I am trying to acheive

class MyCommandData(vtk.vtkDataObject):
    def __init__(self):
        super(MyCommandData, self).__init__(self)
        self.stdin = ''
        self.stdout = ''
        self.stderr = ''
        self.retcode = 0


class MyCommand(vtk.vtkAlgorithm):

    def __init__(self):
        super(MyCommand, self).__init__(self,
                                        nInputPorts=1, inputType='MyCommandData',
                                        nOutputPorts=1, outputType='MyCommandData')

    def FillInputPortInformation(self, port, info):
        if port == 0:
            info.Set(vtk.vtkAlgorithm.INPUT_IS_OPTIONAL(), 1)
        return 1
2

I have make some progress with the following but it thinks my custom data is not define

import vtk
from vtkmodules.util.vtkAlgorithm import VTKPythonAlgorithmBase


class MyCommandData(vtk.vtkDataObject):
    def __init__(self):
        super(MyCommandData, self).__init__()
        self.stdin = ''
        self.stdout = ''
        self.stderr = ''
        self.retcode = 0


class MyCommand(VTKPythonAlgorithmBase):

    def __init__(self):
        super(MyCommand, self).__init__(nInputPorts=1, inputType='MyCommandData',
                                        nOutputPorts=1, outputType='MyCommandData')

    def FillInputPortInformation(self, port, info):
        if port == 0:
            info.Set(vtk.vtkAlgorithm.INPUT_IS_OPTIONAL(), 1)
            info.Set(vtk.vtkDataObject.DATA_TYPE_NAME(),'MyCommandData')
        return 1

    def FillOutputPortInformation(self, port, info):
        if port == 0:
            info.Set(vtk.vtkDataObject.DATA_TYPE_NAME(),'MyCommandData')
        return 1

    def RequestData(self, request, inInfo, outInfo):
        input_info = inInfo[0].GetInformationObject(0)
        input = MyCommandData.GetData(input_info)
        output_info = outInfo.GetInformationObject(0)
        output = MyCommandData.GetData(output_info)
        return 1


a = MyCommand()
b = MyCommand()
b.AddInputConnection(0, a.GetOutputPort())
b.Update()

Output is

2022-01-11 17:34:58.297 (   0.149s) [         4EC3080] vtkDataObjectTypes.cxx:296   WARN| NewDataObject(): You are trying to instantiate DataObjectType "MyCommandData" which does not exist.
2022-01-11 17:34:58.297 (   0.149s) [         4EC3080]vtkDemandDrivenPipeline:615    ERR| vtkCompositeDataPipeline (0x5590416af7b0): Algorithm vtkPythonAlgorithm(0x5590416ae360) did not create output for port 0 when asked by REQUEST_DATA_OBJECT and does not specify a concrete DATA_TYPE_NAME.
3

It is not possible to subclass VTK objects from Python in ways that the C++ code is aware of them as there is no “glue” class which C+±inherits from arbitrary VTK classes and forwards requests to Python code (as is done for VTKPythonAlgorithmBase).