[py] Fix and instructions on importating simulator modules.

Applications/Python/ogs.mesh/CMakeLists.txt

 # Create OpenGeoSys python module
 # https://pybind11.readthedocs.io/en/stable/compiling.html#building-with-cmake
-pybind11_add_module(
-    mesh MODULE ogs_mesh_python_module.cpp OGSMesh.cpp
-)
+pybind11_add_module(mesh MODULE ogs_mesh_python_module.cpp OGSMesh.cpp)
 
 # lld linker strips out PyInit_OpenGeoSys symbol. Use standard linker.
 get_target_property(_link_options mesh LINK_OPTIONS)
@@ -14,7 +12,6 @@ endif()
 target_link_libraries(
     mesh PRIVATE MeshLib BaseLib CMakeInfoLib GitInfoLib tclap
 )
-target_include_directories(mesh  PRIVATE ../../../MeshLib)
 
 # Install into Python module root dir (enables 'import ogs.simulator')
 install(TARGETS mesh LIBRARY DESTINATION ogs)

Applications/Python/ogs.mesh/OGSMesh.h

@@ -29,7 +29,9 @@
 #include "MeshLib/Mesh.h"
 #include "MeshLib/Node.h"
 
-class OGSMesh
+// Needs to be exported, see
+// https://pybind11.readthedocs.io/en/stable/advanced/misc.html#partitioning-code-over-multiple-extension-modules
+class PYBIND11_EXPORT OGSMesh
 {
 public:
     explicit OGSMesh(MeshLib::Mesh* mesh);

Applications/Python/ogs.simulator/CMakeLists.txt

@@ -15,7 +15,7 @@ endif()
 target_link_libraries(
     simulator PRIVATE ApplicationsLib BaseLib CMakeInfoLib GitInfoLib tclap
 )
-target_include_directories(simulator PRIVATE ../../CLI ../ogs.mesh)
+target_include_directories(simulator PRIVATE ../../CLI)
 
 # Install into Python module root dir (enables 'import ogs.simulator')
 install(TARGETS simulator LIBRARY DESTINATION ogs)

Applications/Python/ogs.simulator/ogs_python_module.cpp

@@ -182,7 +182,12 @@ void finalize()
     BaseLib::unsetProjectDirectory();
 }
 
-/// python module name is OpenGeoSys
+/// To use this module import dependencies first:
+///   import ogs.mesh as mesh
+///   import ogs.simulator as sim
+///
+/// See also
+/// https://github.com/pybind/pybind11/issues/1391#issuecomment-912642979
 PYBIND11_MODULE(simulator, m)
 {
     m.attr("__name__") = "ogs.simulator";