> This documentation (http://docs.python.org/library/struct.html)
> claims that an unsigned long is 4 bytes.

I don't think it does, if you read it closely.  Of course, patches to improve the docs are always welcome. :)

If you're looking at the table of format codes, note that it refers to the *standard* size, which is the size used when standard size and alignment are in effect (i.e., when the struct format string starts with '<', '>', etc.).  That standard size is indeed 4 bytes for the 'l' and 'L' codes.