Cross platform doesn’t exists
When you write code in Python you can be almost sure your code will run on different operating systems. I say almost sure, not completely sure, because some of the libraries and packages you are using can have different behaviors on different systems.
But here I found a full incompatibility in the bsddb package on the same Python release but on different operating systems.
First, install Python 2.6.2 on a Windows machine and on a OpenSuse machine.