We have a C++ application, with C++ interfaces changing regularly during development. We also have a C API which is designed to be stable in spite of such changes; the C API is tighly focused on operations which client code might want to do.
Now, we want to add a Python API to make it easy for outside clients (or our own team) to create scripts controlling the application. Given the volatility of the C++ code and the by-design stable nature of the C API, it makes sense to build the Python API over the C one. I know the way to do this is to provide an extension module (implemented in C++) which will be usable in Python and wrap the C API functions.
What I am considering is whether I should make this extension module the Python API (and thus make it as Pythonic as possible), or whether I should keep this an "implementaion detail" of the Python API and build a pure Python module on top of it, which would serve as the actual external API. The extension module would then be a very thing wrapper around the C functions, resigning on being nice Python code.
I see the following pros and cons:
Python API is a C++ extension
This would be more efficient, as there are less intermediary layers. At the same time, it requires boilerplate code to provide Pythonic behaviour in C++, and the code is generally harder to write and maintain (reference counting, pointer tables etc.).
Python API is a module wrapping the C++ extension
This allows us to write Pythonic code in Python, which is easier and less error-prone. It would probably lead to a richer, more complete API as well, since adding functionality is easier and faster in Python than in C++. As a downside, there's runtime and memory overhead of the extra layer, as well as the need to maintain two separate bits of code for one thing.
My primary question is: are there any obvious upsides or downsides to some of the approaches that I failed to consider, especially ones that make one choice clearly superior to the other? Also, is there a widely accepted "best practice" for this type of thing? Or a "checklist" to help choose the correct approach for a particular situation?