Recreate file associations?

[random832 at fastmail.us]

I installed Python 2.1 for historical interest and it associated python
files with the python 2.1 interpreter. I installed 3.4 afterwards (I had
3.3 as my latest python version before) expecting this to fix it, but it
left it alone. Even deleting all the Python associations from the
registry and then repairing 3.4, it didn't create them. How do I get it
to make the file associations the same as the first time I installed
Python 3?