Python 3 had massive breaking changes, especially in the way it handles the string <-> byte conversion at the edge of the application. It's very easy to write a

Python 3 had massive breaking changes, especially in the way it handles the string <-> byte conversion at the edge of the application. It's very easy to write a Python 2 application that works on ASCII and fails as soon as someone inserts umlauts, and very hard for Python 3.