Determining when a file is an Open Office Document

[tubby]

Silly question, but here goes... what's a good way to determine when a 
file is an Open Office document? I could look at the file extension, but 
it seems there would be a better way. VI shows this info in the files:

mimetypeapplication/vnd.oasis.opendocument.textPK
mimetypeapplication/vnd.oasis.opendocument.presentationPK
etc.

Not really a Python specific question but, how do you guys do this sort 
of thing? I've figured out how to break out the content.xml file in the 
new OOo XML format, and do re searching and matching on that, now I just 
need a fast, reliable way to determine when I need to do that versus 
just reading the file.

Thanks,
Tubby