ENH: Add configuration to disable Python factory loading

Wrapping/Generators/Python/Tests/CMakeLists.txt

@@ -20,6 +20,7 @@ itk_python_add_test(NAME PythonComplex COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/compl
 itk_python_add_test(NAME PythonHelperFunctions COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/helpers.py)
 itk_python_add_test(NAME PythonLazyModule COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/lazy.py)
 itk_python_add_test(NAME PythonNoLazyModule COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/nolazy.py)
+itk_python_add_test(NAME PythonNoDefaultFactories COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/nodefaultfactories.py)
 itk_python_add_test(NAME PythonDICOMSeries COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/dicomSeries.py
               DATA{${ITK_DATA_ROOT}/Input/DicomSeries/Image0075.dcm}
               DATA{${ITK_DATA_ROOT}/Input/DicomSeries/Image0076.dcm}

Wrapping/Generators/Python/Tests/nodefaultfactories.py

@@ -0,0 +1,25 @@
+# ==========================================================================
+#
+#   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 itkConfig
+
+# Override environmental variable default to ignore factories at load time
+itkConfig.DefaultFactoryLoading = False
+import itk
+
+# Verify the object factory singleton is empty
+assert len(itk.ObjectFactoryBase.GetRegisteredFactories()) == 0

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

@@ -26,6 +26,7 @@
 import pkg_resources
 
 import itkConfig
+from itkConfig import DefaultFactoryLoading as _DefaultFactoryLoading
 from itk.support.template_class import itkTemplate
 
 
@@ -236,7 +237,8 @@ def itk_load_swig_module(name: str, namespace=None):
     # for some base class(es) defined in the current module.
     # For instance, ITKImageIOBase will load any modules defining
     # ImageIO objects for reading different image file types.
-    load_module_needed_factories(name)
+    if _DefaultFactoryLoading:
+        load_module_needed_factories(name)
 
     for snakeCaseFunction in l_data.get_snake_case_functions():
         namespace[snakeCaseFunction] = getattr(l_module, snakeCaseFunction)

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

@@ -17,6 +17,7 @@
 # ==========================================================================*/
 import types
 from itk.support import base
+from itkConfig import DefaultFactoryLoading as _DefaultFactoryLoading
 
 # Needed to avoid problem with aliasing of itk.set (itkTemplate)
 # inside the itk namespace.  We need to explictly specify the
@@ -139,7 +140,8 @@ def __getattribute__(self, attr):
                     for k, v in namespace.items():
                         setattr(self, k, v)
                     value = namespace[attr]
-                    base.load_module_needed_factories(module)
+                    if _DefaultFactoryLoading:
+                        base.load_module_needed_factories(module)
                 else:  # one of the other threads that had been blocking
                     # waiting for first thread to complete. Now the
                     # attribute is REQUIRED to be available

Wrapping/Generators/Python/itkConfig.py.in

@@ -69,6 +69,7 @@ def _get_environment_boolean(environment_var: str, default_string: str) -> bool:
     return bool(_strtobool(default_string))
 
 
+DefaultFactoryLoading: bool = _get_environment_boolean("ITK_PYTHON_DEFAULTFACTORYLOADING", "True")
 LazyLoading: bool = _get_environment_boolean("ITK_PYTHON_LAZYLOADING", "True")
 NotInPlace: bool = _get_environment_boolean("ITK_PYTHON_NOTINPLACE", "False")
 del _get_environment_boolean