[Python-Dev] Exception Reorg PEP revised yet again

Thomas Heller theller at python.net
Fri Aug 12 10:42:09 CEST 2005

Brett Cannon <bcannon at gmail.com> writes:

> On 8/10/05, Raymond Hettinger <raymond.hettinger at verizon.net> wrote:
>> > > Then I don't follow what you mean by "moved under os".
>> >
>> > In other words, to get the exception, do ``from os import
>> > WindowsError``.  Unfortunately we don't have a generic win module to
>> > put it under.  Maybe in the platform module instead?
>> -1 on either.  The WindowsError exception needs to in the main exception
>> tree.  It occurs in too many different modules and applications.  That
>> is a good reason for being in the main tree.
> Where is it used so much?  In the stdlib, grepping for WindowsError
> recursively in Lib in 2.4 turns up only one module raising it
> (subprocess) and only two modules with a total of three places of
> catching it (ntpath once, urllib twice).  In Module, there are no
> hits.

I don't know how you've been grepping, but the Python api functions to
raise WindowsErrors are named like PyErr_SetFromWindowsErr() or so.

Typically, WindowsErrors are raised when Win32 API functions fail.
In the core extension modules, I find at least mmapmodule.c,
posixmodule.c, _subprocess.c, and _winreg.c raising them.  It may be a
bit hidden, because the docs for _winreg mention only EnvironmentError,
but they are wrong:

Python 2.5a0 (#60, Jul  4 2005, 19:53:27) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import _winreg
>>> _winreg.OpenKey(_winreg.HKEY_CLASSES_ROOT, "blah")
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
WindowsError: [Errno 2] Das System kann die angegebene Datei nicht finden

>> If the name bugs you, I would support renaming it to PlatformError or
>> somesuch.  That would make it free for use with Mac errors and Linux
>> errors.  Also, it wouldn't tie a language feature to the name of an
>> MS product.
> I can compromise to this if others prefer this alternative.  Anybody
> else have an opinion?

Win32 has the FormatError() api to convert error codes into descriptions
- these descriptions are very useful, as are the error codes when you
catch errors in client code.

I would say as long as the Python core contains win32 specific modules
like _winreg WindowsError should stay.  For the name, I have no
preference but I see no need to change it.


PS: For ctypes, it doesn't matter if WindowsError stays or not.  No
problem to invent my own WindowsError if it goes away.

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