Details on exceptions

[Derek Fountain]

Are the details of the builtin exceptions laid out anywhere? I was looking
though the O'Reilly Nutshell book, which informs me that errors with file
objects raise the builtin exception IOError. However, it doesn't describe
this exception in the same way it describes, for example, the OSError
exception. How do I get the actual error code from IOError of what went
wrong?

I did a search on the Python docs, and couldn't find the information either.
So either the information is well hidden for some reason, or I've missed
some very important information on the standardisation of exception
handling techniques.