BUG: Import C module from Python submodule

Trigger the C module initialization funcitons of the submodule stored in
the module binary.

To address:

  distributed.protocol.core - CRITICAL - Failed to deserialize
  Traceback (most recent call last):
    File "/home/matt/bin/miniconda3/envs/dask/lib/python3.7/site-packages/distributed/protocol/core.py", line 130, in loads
      value = _deserialize(head, fs, deserializers=deserializers)
    File "/home/matt/bin/miniconda3/envs/dask/lib/python3.7/site-packages/distributed/protocol/serialize.py", line 303, in deserialize
      return loads(header, frames)
    File "/home/matt/bin/miniconda3/envs/dask/lib/python3.7/site-packages/distributed/protocol/serialize.py", line 65, in pickle_loads
      return pickle.loads(x, buffers=buffers)
    File "/home/matt/bin/miniconda3/envs/dask/lib/python3.7/site-packages/distributed/protocol/pickle.py", line 66, in loads
      return pickle.loads(x)
    File "/home/matt/bin/miniconda3/envs/dask/lib/python3.7/site-packages/itk/itkPyBufferPython.py", line 13, in <module>
      from . import _itkPyBufferPython
  ImportError: cannot import name '_itkPyBufferPython' from 'itk' (unknown location)

Addresses #1517

Author: thewtex

Wrapping/Generators/CMakeLists.txt

@@ -119,7 +119,7 @@ macro(itk_wrap_submodule_all_generators module)
     itk_wrap_submodule_DOC("${module}")
   endif()
   if(${module_prefix}_WRAP_PYTHON AND WRAPPER_LIBRARY_PYTHON)
-    itk_wrap_submodule_python("${module}")
+    itk_wrap_submodule_python("${module}" "${WRAPPER_LIBRARY_NAME}")
   endif()
   if(${module_prefix}_WRAP_TCL AND WRAPPER_LIBRARY_TCL)
     itk_wrap_submodule_tcl("${module}")

Wrapping/Generators/Python/CMakeLists.txt

@@ -331,7 +331,7 @@ macro(itk_end_wrap_module_python)
   set(ITK_WRAP_PYTHON_PROCESS_SWIG_INPUTS ON)
   foreach(source ${WRAPPER_LIBRARY_SWIG_INPUTS})
     get_filename_component(base_name ${source} NAME_WE)
-    itk_wrap_submodule_python("${base_name}")
+    itk_wrap_submodule_python("${base_name}" "${WRAPPER_LIBRARY_NAME}")
     itk_end_wrap_submodule_python("${base_name}")
   endforeach()
   set(ITK_WRAP_PYTHON_PROCESS_SWIG_INPUTS OFF)
@@ -623,11 +623,11 @@ macro(ADD_PYTHON_CONFIG_TEMPLATE base_name wrap_class swig_name template_params)
 endmacro()
 
 
-macro(itk_wrap_submodule_python module)
-  set(ITK_WRAP_PYTHON_SWIG_EXT "\n")
+macro(itk_wrap_submodule_python submodule module)
+  set(ITK_WRAP_PYTHON_SWIG_EXT "%pythonbegin %{\nfrom . import _${module}Python\n%}\n\n")
 
   # register the module for the lib module
-  set(ITK_WRAP_PYTHON_LIBRARY_IMPORTS "${ITK_WRAP_PYTHON_LIBRARY_IMPORTS}from itk.${module}Python import *\n")
+  set(ITK_WRAP_PYTHON_LIBRARY_IMPORTS "${ITK_WRAP_PYTHON_LIBRARY_IMPORTS}from itk.${submodule}Python import *\n")
 
 endmacro()
 

Wrapping/Generators/Python/PyBase/pyBase.i

@@ -1,5 +1,9 @@
 %module(package="itk") pyBasePython
 
+%pythonbegin %{
+from . import _ITKPyBasePython
+%}
+
 %include <exception.i>
 %include <typemaps.i>