Upgrading python3.4 to python3.6 on ubuntu breaks pip

I managed to solve it without installing anything from sources.
Here’s what I did:

1. First, install pip for Python3.x (for some weird reason I didn’t have it…)

   $ sudo apt-get install python3-pip
   

   It is an old version…

   $ pip3 --version
   pip 1.5.4 from /usr/lib/python3/dist-packages (python 3.4)
   

2. … so upgrade it to the latest

   $ sudo pip3 install --upgrade pip
   

   Now it is much better

   $ sudo pip3 --version
   pip 9.0.1 from /usr/local/lib/python3.4/dist-packages (python 3.4)
   

3. Then upgrade virtualenvvwrapper

   $ sudo pip3 install --upgrade virtualenvwrapper
   # ...
   Successfully installed pbr-3.0.1 six-1.10.0 stevedore-1.22.0 virtualenv-15.1.0 virtualenv-clone-0.2.6 virtualenvwrapper-4.7.2
   

4. Now creating a new virtualenv works:

   $ mkvirtualenv -p `which python3.6` <VIRTUALENV_NAME>
   

   pip also works:

   $ pip install django
   # ...
   Successfully installed django-1.11.2 pytz-2017.2
   
   $ pip freeze
   Django==1.11.2
   pytz==2017.2
   

Note: Now I realize it’s a bit more than what you asked for, but (without knowing where exactly you failed) I guess you should be OK after step 2.