There are a couple of ways to solve this problem
Pyinx - a pretty lightweight tool that allows you to call Python from withing the excel process space http://code.google.com/p/pyinex/
I've used this one a few years ago (back when it was being actively developed) and it worked quite well
If you don't mind paying, this looks pretty good
https://datanitro.com/product.html
I've never used it though
Though if you are already writting in Python, maybe you could drop excel entirely and do everything in pure python? It's a lot easier to maintain one code base (python) rather than 2 (python + whatever excel overlay you have).
If you really have to output your data into excel there are even some pretty good tools for that in Python. If that may work better let me know and I'll get the links.