[Python-Dev] "DOS" error codes, WindowsError, and errno

["Martin v. Löwis"]

Mark Hammond wrote:
> I guess "too late" is purely a judgement call about breaking existing code.
> One thing to our advantage is that I believe the most common errno
> explicitly checked for will be ENOENT, which happily has the same value as
> ERROR_FILE_NOT_FOUND.  [Actually, checking 2 *or* 3 (ERROR_PATH_NOT_FOUND)
> is also common - but ESRCH==3, which sounds reasonable]

The strerror for ESRCH is "No such process", which isn't really that
reasonable. Breakage would occur, because people might currently check
for ENOENT (or any other specific error code); if they don't see that
specific error code, they will assume it is a "real" error.

That said: I would actually expect that it is infrequent that people
do look at the errno of a WindowsError, so breakage might be small.

> Another way forward may be to issue a warning whenever '.errno' or '[0]' is
> referenced from WindowsError, noting that the semantics are soon to change,
> and to use the new attribute if they really do want a win32 error code.  I'm
> not sure how practical that is though...

It would need to get suppressed when the value is merely displayed,
atleast in the default __str__ implementation.

Regards,
Martin