WIP bpo-34589: Move locale coercion back to the CLI app by ncoghlan · Pull Request #9257 · python/cpython (original) (raw)

The issue I had with doing the message formatting in _Py_CoerceLegacyLocale is coping with the dynamic memory allocation needed (you could use a statically allocated array instead, but that's a different kind of ick).

However, I'm thinking there may be a better way to defer the rendering of the warning while still only needing one field on the main struct: make the field a function pointer accepting a C output stream that gets called instead of a C string that gets printed, and then in the warning rendering function, substitute the actual current locale into the message, rather than saving the name of the coercion target (This is all internal to the CPython command line app, so we don't need to worry about intervening locale changes).

With that change, this would just be a standard C callback API, rather than something that tightly couples the code that determines the warning is needed to the code that actually prints it after the standard streams are configured.