Good evening,
today i messed up my laptop trying to install some packages for python 3.5.2. I tried to install the correct pip version but i missed something and now
I'd highly recommend using virtualenv, and never modifying the system python, except to install pip and virtualenv if necessary.
As was alluded to above, many OSes count on having a working python2 in order to function.
So...
apt-get remove python3
apt-get install python3
pip3 install virtualenv
virtualenv -p python3 venv
. venv/bin/activate
# now you are in a nice python3 world, completely isolated from system python
# remember to say . venv/bin/python every time you do anything
# or you can even add it to your .bashrc