sim.chunk_layout is not accessible in Python if not specified at class instantiation time

[bencbartlett]

If a meep.Simulation object is created without specifying chunk_layout, then the default logic for choosing chunk divisions is invoked when sim.init_sim() is called. However, the chunk_layout attribute on the Python Simulation object is not updated to reflect this change and will still read as None.

When converting from a Python meep.BinaryPartition object, py_bp_to_bp() is called to convert the Python object into a C++ object. It would be useful to have the inverse operation present with a bp_to_py_bp() function, perhaps as a class construction method to live on meep.BinaryPartition. Then in Simulation._init_structure() at line 1709, this function could be called to update the Simulation.chunk_layout attribute:

if self.chunk_layout is None:
  self.chunk_layout = mp.BinaryPartition.from_cpp_object(...)

[stevengj]

Probably the code would go in python/typemap_utils.cpp. Once you have the function PyObject *binarypartition_cpp_to_py(...) or whatever it is called, SWIG should handle it automatically.

You may also need some refactoring in the structure constructor to save the binary partition it creates.