Serhiy Storchaka added the comment:
> See issue27213. Maybe fast call with keyword arguments would avoid the creation of a dict.

In a first verison of my implementation, I used dictionary items
stored a a list of (key, value) tuples in the same PyObject* C array
than positional parameters.

But in practice, it's very rare in the C code base to have to call a
function with keyword parameters, but most functions expect keyword
parameters as a dict. They are implemented with
PyArg_ParseTupleAndKeywords() which expects a dict.