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'