cet-is » fhicl » fhicl-cpp

We would like to meet to discuss more details about the requirements, such as what dependencies are acceptable for this new facility. We will follow up through email.

The attached files have been provided by Herb for creating a Python dictionary from a C++ fhicl::ParameterSet object.

Herb, the code contains what we would hope to see--a final dictionary that is independent of the fhiclcpp details. We would be in a better position to take on this facility if you could convert the code to using the fhicl::detail::ParameterSetWalker interface, which admittedly is not well-known. You would write a derived class (e.g. PSetToPythonDict), which overrides functions for processing FHiCL atoms, sequences, and tables. After the derived class is defined, you could do (e.g.):

PSetToPythonDict converter;
pset.walk(converter);
PyObject* pset_dict = converter.result();

without having to do any explicit tree-walking yourself.

Unfortunately, we do not have the effort available to make this conversion ourselves. However, by making this conversion, we can then adopt the code and guarantee that any future changes made in the fhicl::ParameterSet implementation will be appropriately reflected in the Python dictionary.

Please look at the documentation in fhiclcpp/detail/ParameterSetWalker.h and/or contact us with questions. Note that the fhicl::ParameterSet::walk method is currently private (and spelled with a trailing underscore). However, there is no reason it cannot be made public.

Your code is a big step forward.

We intend to move item 2 to its own issue since it involves moving some art infrastructure to canvas, as well as new development. Items 1 and 3 are provided by the code that Herb provided. We will integrate Herb's Python extension module to fhicl-cpp, which also involves moving the Python dependency from canvas down to fhicl-cpp.

Largely implemented with commit fhicl-cpp:2ce61ba.

Some discussion is required regarding how the module library should be packaged/"set up" for use.

Implemented with commit fhicl-cpp:b4cc5ad. The extension module is called fhicl, and PYTHONPATH is appropriately set whenever the fhiclcpp UPS product is set up.