Comment by gilest

You can do almost exactly that in Resolver One (http://www.resolversystems.com/), which has got a Python console as well as allowing Python functions and Python syntax in the grid. It's a separate spreadsheet program, though, not an Excel plug-in.

Alternatively, there's PyXLL (http://www.pyxll.com/), which lets you write Excel user-defined functions in Python, but doesn't have a console.

(Full disclosure: I work for Resolver Systems.)