I have been playing with this code and it's been lots of fun.
I've hacked it into a functional spreadsheet in (according to eric3) 508 lines of non-doc code, of which 244 are generated by pyuic.
Here's my code so far (requires PyQt). Give it a look, I think it's kinda nice.
The only hard part I wrote (at least hard for me) was the cell dependency and recalculation support.
There's a test file you can use, too.
It is trivial to add functions you can use in the cells, just lookup python docs for eval() and check engine.py.
To use it, unpack it, and from the directory it creates run
I don't plan to make it a real spreadsheet, but it should be fun to hack on :-)