Make virtualenvwrapper use brew-ed python instead of system python on OS X 10.9

Question

Question

Why does $ mkvirtualenv test use the system python (v2.7.6) instead of the brew-ed python (2.7.8) and how do I configure virtualenvwrapper to use the desired python?

System Setup

I'm using OS X 10.9.5 with a homebrew install of python (v2.7.8). I have a system wide install of virtualenv and virtualenvwrapper. My shell is ZSH via oh-my-zsh using the virtualenvwrapper plugin (although I've tried pulling out the plugin and sourcing virtualenvwrapper.sh manually and I get the same behavior).

Demo

This 2.7.8 is the python interpreter I get from a shell

$ echo $PATH
/usr/local/bin:/usr/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin

$ which python
/usr/local/bin/python

$ python
Python 2.7.8 (default, Aug 24 2014, 21:26:19)
...

I have the following environment set in at the top of my .zshrc (before virtualenvwrapper is sourced) and have matched them all to the output of $ printenv to confirm they are getting set correctly

export PATH="/usr/local/bin:/usr/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin"

export WORKON_HOME=$HOME/.virtualenvs
export PROJECT_HOME=$HOME/Projects/Python
# this is the location shown above to be v2.7.8
export VIRTUALENVWRAPPER_PYTHON=/usr/local/bin/python 
export VIRTUALENVWRAPPER_VIRTUALENV=/usr/local/bin/virtualenv 
export PIP_DOWNLOAD_CACHE=$HOME/.pip/download_cache
export PIP_VIRTUALENV_BASE=$WORKON_HOME

Despite the correct $PATH and the explicit override to use the python interpreter I know is v2.7.8 any mkproject gets the default system python:

$ mkvirtualenv test
....

(test)$ python
Python 2.7.6 (default, Mar 18 2014, 15:05:23)
...

Workaround

I have found an infuriating (in that it seems it should change nothing yet does) work around

$ mkvirtualenv -p `which python` test
...

(test)$ python
Python 2.7.8 (default, Aug 24 2014, 21:26:19)
...

So why in the world are these environment variables not getting used despite being set and it having the clear possibility of working as shown in the work around??

How did you install virtualenv itself? On my system, the virtualenv script has as its shebang /usr/bin/python, which might explain your issue. Maybe try removing that and re-installing it via brew? — Daniel Roseman
– Daniel Roseman, Commented Sep 21, 2014 at 21:54
@DanielRoseman Looks like that may have been it. Are all of these various environment vars merely placebos? — Finn
– Finn, Commented Sep 23, 2014 at 1:23

vgel · Accepted Answer · 2014-09-21 22:21:09Z

By default, virtualenv will use the python binary it was installed with, not the python binary that shows up first in the path.

virtualenv --help
...
  -p PYTHON_EXE, --python=PYTHON_EXE
                        The Python interpreter to use, e.g.,
                        --python=python2.5 will use the python2.5 interpreter
                        to create the new environment.  The default is the
                        interpreter that virtualenv was installed with
                        (/usr/bin/python)

Your best bet is probably to uninstall virtualenvwrapper and then reinstall it with the pip living in your brewed Python's install directory.

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Make virtualenvwrapper use brew-ed python instead of system python on OS X 10.9

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