PyArg_ParseTupleAndKeywords and fields take (non-const) char *keywords[]

[iritkatriel]

See python/cpython#65210.

[gvanrossum]

The best explanation I've found is this message from Martin von Loewis. There are a few messages after that where people are trying to come up with a solution, unfruitfully; after that the discussion degenerates into a flame war about C++.

I'm actually still not sure what we could do differently in the 4.0 API -- make it const * const * keywords?

[serhiy-storchaka]

It explains why char ** cannot be implicitly converted to const char **, but not why it cannot be implicitly converted to const char * const *. And in C++ (which in general is more strictly types than C) such implicit conversion is supported. Why it does not work in C? The answer is because. The C rules are simpler than the C++ rules, so they did not bother to add special rules for such implicitly conversion, even if this causes some inconvenience in practice. I only hope that they will change this in future versions.

I think that we can fix this in C++ in compatible way, but for C we can only provide a lever to chose between const char * const * and char * const * (the latter is compatible with char **). It could also make transition to future incompatible C API (if we decide to break it) simpler.

[serhiy-storchaka]

See python/cpython#105958 as example.