ENH: Python wrapping reads VLV pixel type correctly

The test file is produced by 3D Slicer, which is a saved
segmentation of mouse tibia (down-sampled for test).

Wrapping/Generators/Python/Tests/CMakeLists.txt

@@ -81,3 +81,13 @@ itk_python_add_test(NAME PythonMultiprocessLazyLoad
       COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/multiprocess_lazy_loading.py
         DATA{${WrapITK_SOURCE_DIR}/images/cthead1.png} DATA{${WrapITK_SOURCE_DIR}/images/templated_pipeline.png} DATA{${WrapITK_SOURCE_DIR}/images/2th_cthead1.png}
     )
+
+# Test proper reading and writing of VariableLengthVector
+itk_python_add_test(NAME PythonVLVReadWriteTest
+    TEST_DRIVER_ARGS
+      --compare ${ITK_TEST_OUTPUT_DIR}/TestVLV.seg.nrrd DATA{${WrapITK_SOURCE_DIR}/images/TestVLV.seg.nrrd}
+    COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/readWriteVLV.py
+      DATA{${WrapITK_SOURCE_DIR}/images/TestVLV.seg.nrrd}
+      ${ITK_TEST_OUTPUT_DIR}/TestVLV.seg.nrrd
+      59 85 58 5
+    )

Wrapping/Generators/Python/Tests/readWriteVLV.py

@@ -0,0 +1,31 @@
+# ==========================================================================
+#
+#   Copyright NumFOCUS
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#          http://www.apache.org/licenses/LICENSE-2.0.txt
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+#
+# ==========================================================================*/
+
+import itk
+import sys
+
+if len(sys.argv) < 3:
+    print("Usage: " + sys.argv[0] + " in.seg.nrrd out.seg.nrrd")
+    sys.exit(1)
+
+itk.auto_progress(2)
+
+test_image = itk.imread(sys.argv[1], pixel_type=itk.VariableLengthVector[itk.UC])
+for i in range(len(sys.argv) - 3):
+    assert test_image.shape[i] == int(sys.argv[i + 3])
+itk.imwrite(test_image, sys.argv[2], compression=True)

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

@@ -951,7 +951,15 @@ def imread(
         # Increase dimension if last dimension is not of size one.
         if increase_dimension and image_IO.GetDimensions(dimension - 1) != 1:
             dimension += 1
-        ImageType = itk.Image[pixel_type, dimension]
+        is_vlv = False
+        try:
+            is_vlv = itk.template(pixel_type)[0] is itk.VariableLengthVector
+        except KeyError:
+            pass
+        if is_vlv:
+            ImageType = itk.VectorImage[itk.template(pixel_type)[1][0], dimension]
+        else:
+            ImageType = itk.Image[pixel_type, dimension]
         reader = template_reader_type[ImageType].New(**kwargs)
     else:
         reader = template_reader_type.New(**kwargs)

Wrapping/images/TestVLV.seg.nrrd.sha512

@@ -0,0 +1 @@
+9ad6479c834f2280bd2641caa7160e0016a340aa9fbf88f5afa5d7101ffbaaab7b72194a7e8678b4ffca89a25be6f370e19cf41d0b3c811986d5a49a4272929e