Originally Posted by m0ngr31
How hard would it be to be able use this to update the meta information inside a mobi (like mobi2mobi) instead of unpacking it?
It would need a whole lot of new code, I think. Extracting to files, or stripping out sections is very different to re-writing (say) the EXTH section.
But this is probably you best place to start if you want to have a stand-alone modern python-based mobi2mobi kind of function.
The other alternative would be the calibre source code, which (obviously) already has code to create Mobipocket format files.