pessheet, a Python extendable spreadsheet

Somtimes a spreadsheet is the best way to work with a calculation. But working 
inside a spreadsheet, sometimes you wish you could create just the function 
you need. pessheet will help you. You have one tab for the spreadsheet, and 
one tab for a python script that defines the functions. 

pessheet can export the spreadsheet as a dot file to be used with graphvis to 
visualize the calculation graph. 

pessheet can also export the spreadsheet as a python script, to be used as a 
starting point to convert the spreadsheet calculation into a program. 

It is still version 0.something low, and has quite a few rough edges. The code 
is not to look at for the faint of heart. But it is possible to use it for 
real work. 

pessheet uses wxPython. 

The logic part is originally based on a comment at 
http://code.activestate.com/recipes/355045/, although much of it has been 
modified. 

I wouldn't even have started if I hadn't seen the spreadsheet example at 
http://www.zetcode.com/wxpython/skeletons/