There are custom Argument Clinic converters that define format_unit but omit parse_arg. As a result, generation of positional argument parsers is forced to back up from the fastest possible _PyArg_CheckPositional to slower _PyArg_ParseStack-based format strings.

Here is a list of such classes (and fixing PRs except complex cases):

• Modules\_multiprocessing\multiprocessing.c (gh-94517)

  • HANDLE_converter

• Modules\_multiprocessing\semaphore.c

  • SEM_HANDLE_converter

• Modules\overlapped.c (gh-94516)

  • OVERLAPPED_converter
  • HANDLE_converter
  • ULONG_PTR_converter
  • DWORD_converter
  • BOOL_converter

• Modules\posixmodule.c:

  • pid_t_converter
  • idtype_t_converter
  • id_t_converter
  • intptr_t_converter
  • Py_off_t_converter

• Modules\resource.c (gh-94515)

  • pid_t_converter

• PC\msvcrtmodule.c (gh-94514)

  • HANDLE_converter

• PC\winreg.c (gh-94513)

  • REGSAM_converter
  • DWORD_converter
  • HKEY_converter

An example of such a converter:

class BOOL_converter(CConverter):
    type = 'BOOL'
    format_unit = 'i'

class pid_t_converter(CConverter):
    type = 'pid_t'
    format_unit = '" _Py_PARSE_PID "'

I'm going to teach all of them about low-level generation by replacing manual format_unit definitions with:

• inheritance from a corresponding builtin converter where possible
• and custom parse_args in other places.

For the example it gives:

class BOOL_converter(int_converter):
    type = 'BOOL'

class pid_t_converter(CConverter):
    type = 'pid_t'
    # Left as a backup for potential complex cases
    format_unit = '" _Py_PARSE_PID "'

    def parse_arg(self, argname, displayname):
        return """
            {paramname} = PyLong_AsPid({argname});
            if ({paramname} == -1 && PyErr_Occurred()) {{{{
                goto exit;
            }}}}
            """.format(argname=argname, paramname=self.parser_name)