FormatMessage() in python, for system messages.

formatmessagesystem.py

__all__ = (
    FormatMessageSystem,
    LCID_ENGLISH,
    LCID_NEUTRAL,
)

import ctypes
import ctypes.wintypes

LANG_NEUTRAL = 0x00
SUBLANG_NEUTRAL = 0x00
SUBLANG_DEFAULT = 0x01

LANG_ENGLISH = 0x09
SUBLANG_ENGLISH_US = 0x01
def MAKELANGID(primary, sublang):
    return (primary & 0xFF) | (sublang & 0xFF) << 16

LCID_ENGLISH = MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US)
LCID_DEFAULT = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT)
LCID_NEUTRAL = MAKELANGID(LANG_NEUTRAL, SUBLANG_NEUTRAL)
assert LCID_NEUTRAL == 0

FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x00000100
FORMAT_MESSAGE_FROM_SYSTEM = 0x00001000
FORMAT_MESSAGE_IGNORE_INSERTS = 0x00000200

# Note: You probably want to use the builtin ctypes.FormatError instead: https://docs.python.org/3/library/ctypes.html#ctypes.FormatError
# CPython impl: https://github.com/python/cpython/blob/13c1c3556f2c12d0be2af890fabfbf44280b845c/Modules/_ctypes/callproc.c#L254
def FormatMessageSystem(id, langid=LCID_ENGLISH):
    sys_flag = FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS
    
    bufptr = ctypes.wintypes.LPWSTR()
    
    chars = ctypes.windll.kernel32.FormatMessageW(sys_flag, None, id, langid, ctypes.byref(bufptr), 0, None)
    if chars == 0:
        chars = ctypes.windll.kernel32.FormatMessageW(sys_flag, None, id, LCID_NEUTRAL, ctypes.byref(bufptr), 0, None)
        if chars == 0:
            #XXX: You probably want to call GetLastError() here
            return "FormatMessageW failed"

    val = bufptr.value[:chars]
    
    ctypes.windll.kernel32.LocalFree(bufptr)

    return val

in case it might be useful to anyone else, it looks like ctypes has this functionality built in:
https://docs.python.org/3/library/ctypes.html#ctypes.FormatError

Huh, good catch, it does, and apparently has since 2.5. CPython source: https://github.com/python/cpython/blob/13c1c3556f2c12d0be2af890fabfbf44280b845c/Modules/_ctypes/callproc.c#L254

I suppose this Python implementation would be useful if you wanted a specific language.