I have been putting lots of love into Aranduka an eBook manager, (which is looking very good lately, thanks!), and I didn't want it to also be an eBook reader.
But then I thought... how hard can it be to read ePub? Well, it's freaking easy!
Here's a good start at stackoverflow.com but the short of it is... it's a zip with some XML in it.
One of those XML files tells you where things are, one of them is the TOC, the rest is just a small static collection of HTML/CSS/images.
So, here are the ingredients to roll-your-own ePub reader widget in 150 LOC:
Use python's zipfile library to avoid exploding the zip (that's lame)
Use Element Tree to parse said XML files.
Use PyQt's QtWebKit to display said collection of XML/CSS/Images
Use this recipe to make QtWebKit tell you when it wants something from the zipfile.
Plug some things to others, shake vigorously, and you end up with this:
It doesn't display the cover.
It only shows the top level of the table of contents.
I only tested it on two books ;-)
It sure can use a lot of refactoring!
Neither should be terribly hard to do.