Yes its painful to upgrade when the language changes. 2.7 to 3 is a fair change but who moved from php4 to 5? It happens. At least the language didnt die off like VB6 to .net.
I have some personal projects in python 2.7, one because it runs faster in v2 than 3 but if I need to update it I will. Most of the code will work already with little modification and v3 has fixed a few irritating problems.