Install yolk automatically each time you create a virtual env via postmkvirtualenv file

postmkvirtualenv.sh

#!/bin/bash
# This hook is run after a new virtualenv is activated.
PYTHON_VERSION=`python -c 'import sys
print (sys.version_info.major)'`
case $PYTHON_VERSION in
  2)
    echo "Version 2+"
    pip install yolk
    ;;
  3)
    echo "Version 3+"
    pip install --upgrade yolk3k
    ;;
  *)
    echo "Wrong version or no python, skipping"
    ;;
esac