COMP: ITK_WRAP_PYTHON_VERSION is used for remote modules

The remote modules need ITK_WRAP_PYTHON_VERSION defined in the ITKConfig.cmake and
also for embedded ITK builds.  The variable must be set before the
remote modules are processed.

CMake/ITKConfig.cmake.in

@@ -141,4 +141,4 @@ set(ITK_WRAP_complex_double @ITK_WRAP_complex_double@)
 set(ITK_WRAP_IMAGE_DIMS "@ITK_WRAP_IMAGE_DIMS@")
 set(ITK_WRAP_VECTOR_COMPONENTS "@ITK_WRAP_VECTOR_COMPONENTS@")
 
-set(ITK_WRAP_PYTHON_VERSION "@Python3_VERSION@")
+set(ITK_WRAP_PYTHON_VERSION "@ITK_WRAP_PYTHON_VERSION@")

CMake/ITKSetPython3Vars.cmake

@@ -21,6 +21,11 @@ if(PYTHON_DEVELOPMENT_REQUIRED)
 else() # if not PYTHON_DEVELOPMENT_REQUIRED, just find some version of Python (don't need to be as specific)
   find_package(Python3 COMPONENTS Interpreter)
 endif()
+if(ITK_WRAP_PYTHON)
+  set(ITK_WRAP_PYTHON_VERSION "${Python3_VERSION}")
+else()
+  set(ITK_WRAP_PYTHON_VERSION "ITK_WRAP_PYTHON=OFF")
+endif()
 if(NOT Python3_EXECUTABLE AND _specified_Python3_EXECUTABLE) # workaround for cases where FindPython3 fails to set correctly
   set(Python3_EXECUTABLE ${_specified_Python3_EXECUTABLE} CACHE INTERNAL
     "Path to the Python interpreter" FORCE)

CMakeLists.txt

@@ -489,6 +489,20 @@ mark_as_advanced(ITK_USE_FLOAT_SPACE_PRECISION)
 option(DISABLE_MODULE_TESTS "Disable all ITK module tests in `test` folder" OFF)
 mark_as_advanced(DISABLE_MODULE_TESTS)
 
+#-----------------------------------------------------------------------------
+# Need to set python variables before remote modules are included.
+if(BUILD_TESTING OR ITK_BUILD_DOCUMENTATION OR ITK_WRAP_PYTHON)
+  set(PYTHON_DEVELOPMENT_REQUIRED ${ITK_WRAP_PYTHON})
+  include(${CMAKE_CURRENT_SOURCE_DIR}/CMake/ITKSetPython3Vars.cmake)
+
+  if(ITK_WRAP_PYTHON AND NOT Python3_INCLUDE_DIRS)
+    message(FATAL_ERROR "Python version ${Python3_VERSION} development environment not found for wrapping.")
+  endif()
+  if(NOT Python3_ROOT_DIR)
+    get_filename_component(Python3_ROOT_DIR ${Python3_EXECUTABLE} DIRECTORY)
+  endif()
+endif()
+
 #-----------------------------------------------------------------------------
 # Configure Eigen3 before ITKModuleEnablement
 # No download or build is performed. Generates Targets and Config.cmake files for Eigen
@@ -568,22 +582,6 @@ endif()
 
 install(FILES "LICENSE" "NOTICE" "README.md" DESTINATION ${ITK_INSTALL_DOC_DIR} COMPONENT Runtime)
 
-if(BUILD_TESTING OR ITK_BUILD_DOCUMENTATION OR ITK_WRAP_PYTHON)
-  set(PYTHON_DEVELOPMENT_REQUIRED ${ITK_WRAP_PYTHON})
-  include(${CMAKE_CURRENT_SOURCE_DIR}/CMake/ITKSetPython3Vars.cmake)
-
-  if(ITK_WRAP_PYTHON AND NOT Python3_INCLUDE_DIRS)
-    message(FATAL_ERROR "Python version ${Python3_VERSION} development environment not found for wrapping.")
-  endif()
-  if(NOT Python3_ROOT_DIR)
-    get_filename_component(Python3_ROOT_DIR ${Python3_EXECUTABLE} DIRECTORY)
-  endif()
-endif()
-
-# Add user-visible cache entry
-set(Python3_ROOT_DIR ${Python3_ROOT_DIR} CACHE PATH
-  "Which installation or virtual environment of Python to use" FORCE)
-
 if(BUILD_TESTING)
   # If building the testing, write the test costs (i.e. time to run)
   # analysis to disk to more easily review long-running test times