bpo-35582: Argument Clinic: inline parsing code for positional parameters. by serhiy-storchaka · Pull Request #11313

bpo-35582: Argument Clinic: inline parsing code for positional parameters. by serhiy-storchaka · Pull Request #11313 · python/cpython

Would it be possible to find a different name for the function? Otherwise, it's unclear what is _PyArg_CheckPositional(). For _PyUnicodeWriter, I used _PyUnicodeWriter_Prepare (macro) and _PyUnicodeWriter_PrepareInternal (func) names.

/* Prepare the buffer to write 'length' characters
   with the specified maximum character.

   Return 0 on success, raise an exception and return -1 on error. */
#define _PyUnicodeWriter_Prepare(WRITER, LENGTH, MAXCHAR)             \
    (((MAXCHAR) <= (WRITER)->maxchar                                  \
      && (LENGTH) <= (WRITER)->size - (WRITER)->pos)                  \
     ? 0                                                              \
     : (((LENGTH) == 0)                                               \
        ? 0                                                           \
        : _PyUnicodeWriter_PrepareInternal((WRITER), (LENGTH), (MAXCHAR))))

/* Don't call this function directly, use the _PyUnicodeWriter_Prepare() macro
   instead. */
PyAPI_FUNC(int)
_PyUnicodeWriter_PrepareInternal(_PyUnicodeWriter *writer,
                                 Py_ssize_t length, Py_UCS4 maxchar);

You may write a static inline function rather than a macro.