Upgrade from 42.3: Python versions?

I successfully upgraded from 42.3 to Leap 15 and it seems to work.
The process of upgrading rather than formatting the root system partition and rewriting has me a bit confused.
In particular it created space problems; I had to delete a lot of stuff to make room.
In particular /usr space for Python now shows:

# ls /usr/lib64/python
python/    python2.7/ python3.4/ python3.6/

Do I need the python 3.4 since I am now on 3.6?

That’s probably just a left-over, empty, directory from 42.3 anyway.

python 3.6 won’t use it in any case.

Partly right, it was left over but not empty; in fact it was registering in disk usage analyzer as being the largest component in lib64.
It contained stuff in directory “site packages” amounting to 400 MB+, which evidently the upgrade did not know how to handle.
I moved the folder out of the system partition and find that this does not prevent the system from booting
However likely at some point down the road will find that a component is missing for an application which needs to be rebuilt.

Well, in my case it was empty.

Maybe you used python-pip to install python packages?
That circumvents openSUSE’s package management completely, so the files will stay when you upgrade (but as I wrote, they won’t be used by the newer python version).

Correct. I will know in future to check whether there is a provided version of a package before using pip.