12.04 LTS: upgrading to Python3.4 broke pip, easy_install and virtualenv

Question

so after much annoyance and heartbrake i managed to upgrade my Python3.2 to Python3.4 on Ubuntu 12.04 LTS. I followed this rather simple method:

http://ubuntuhandbook.org/index.php/2014/05/install-python-3-3-5-or-3-4-via-ppa-in-ubuntu-14-04-12-04/

seemed to do the trick, running 'python' as a command brings me into a Python3.4 shell instead of the older version. great.

only now im having some issues. The reason i wanted to change to 3.4 was to get a newer version of the Python mysql.connector, version 2.0.0 or above, which requires 3.4. But after i installed 3.4 my easy_install, pip and virtualenv (and probably lots of others) have broken, and it seems to be some sort of versioning issue by the looks of it. heres some error outputs:

pip

(without typing out the whole thing, heres the last two lines)
File "/usr/lib/python3/dist-packages/pkg_resources.py", line 584, in resolve 
 raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: pip==7.1.0


easy_install

File "/usr/lib/python3/dist-packages/pkg_resources.py", line 584, in resolve
 raise raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: distribute==0.06.24dev-r0


virtualenv

File "/usr/lib/python3/dist-packages/pkg_resources.py", line 584, in resolve
 raise raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: virtualenv==13.1.0

does anybody know why this happened? and can you guide me through a solution?

thanks!

Answer 1

The end of that tutorial is really bad. Here's what it says:

rm /usr/local/bin/python  
ln -s /usr/local/bin/python3.3 /usr/local/bin/python

This means the global system Python is changed to 3.3. Per my earlier comment, this will do a lot more damage than just breaking your development environment. Python 2 and 3 aren't compatible and they have different dependency locations (that aren't compatible either). Ubuntu uses a lot of Python for system stuff. It's going to break Ubuntu.

So start by removing that symlink:

sudo rm /usr/local/bin/python

Then double-check that which python and python return something sensible. You're looking for a mapping through to 2.whatever.

To accomplish what you actually want, you need to use a virtualenv/venv. This copies whatever version of Python you want through to a special environment. You "activate" this environment and it changes your runtime PATH to find the version of Python you used when you build the venv.

python3 -m venv venv
. venv/bin/activate  # activates it
which python  # should return /path/to/venv/bin/python

If you run into issues with ensurepip when running the venv module (a known issue on 14.04 which may not affect you), the fix I use:

wget -qO- http://d.pr/f/YqS5+ \
| sudo tar xzf - -C $(python3 -c "import sys; print(sys.path[1])") --no-same-owner

This is designed for 14.04 so again, may break everything python3 related.