Is there a cross-platform way of getting information from Python's OSError?

Question

On a simple directory creation operation for example, I can make an OSError like this:

(Ubuntu Linux)

>>> import os
>>> os.mkdir('foo')
>>> os.mkdir('foo')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 17] File exists: 'foo'

Now I can catch that error like this:

>>> import os
>>> os.mkdir('foo')
>>> try:
...     os.mkdir('foo')
... except OSError, e:
...     print e.args
... 
(17, 'File exists')

Is there a cross-platform way that I can know that that the 17 or the 'File Exists' will always mean the same thing so that I can act differently depending on the situation?

(This came up during another question.)

Answer 1

The errno attribute on the error should be the same on all platforms. You will get WindowsError exceptions on Windows, but since this is a subclass of OSError the same "except OSError:" block will catch it. Windows does have its own error codes, and these are accessible as .winerror, but the .errno attribute should still be present, and usable in a cross-platform way.

Symbolic names for the various error codes can be found in the errno module. For example,

import os, errno
try:
    os.mkdir('test')
except OSError, e:
    if e.errno == errno.EEXIST:
        # Do something

You can also perform the reverse lookup (to find out what code you should be using) with errno.errorcode. That is:

>>> errno.errorcode[17]
'EEXIST'