I just started kamailio master branch with app_python3, using the python routing script from source tree `misc/examples/kemi/kamailio-basic-kemi-python.py`. It started fine, so likely you face something related to a python extension you are using. It doesn't seem to have a relation to the C code in Kamailio, therefore I suggest to start a discussion on `sr-users [at] lists.kamailio.org` mailing list to identify the problem, there are many more people using Python then those in the development team.
For not this item is going to be closed, if proves to be something in the code after sorting out on sr-users, then it can be reopened.