> So expat doesn't count as that literally wraps the expat library.

XML parser can be implemented in pure Python. There are a lot of XML parsers 
implemented in different programming languages.

> Random
> also requires accessing the system randomization libraries to work
> properly so I don't think that is a candidate either.

No, random have C implemented some basic methods only for speed. It uses 
time() system function for initial seeding, but time() is accessible from pure 
Python too.

Some OS-specific modules (pwd, grp, spwd, resource, ossaudiodev, etc) can be 
implemented in pure Python on some platforms (using I/O and ioctl on special 
files in /etc, /dev or /proc).