How do I get the current value of "errno"

I know that there's os.strerror to get the error string, and the errno
module gives me all of the mappings like 34 -> ERANGE.  But I have yet
to find out how to check the value of errno in a Python script.

If I'm missing something obvious, please tell me.  But I've been using
Python for about six years now, and I never have found out how to do
this.

Thanks a lot.
-- 
Steve Juranich
Tucson, AZ