virtualenv (isolated virtual environment) for python runtime

refrence: https://virtualenv.pypa.io/en/latest/userguide.html#usage

1. install

#pip install virtualenv

2. create a isolated env

#cd ~
#mkdir -p py_env/dj_1.4
#virtualenv py_env/dj_1.4

3. active env

#. bin/activate

or

#source bin/activate

4. deactivate

#deactivate

5.pip install demo

Reference: https://pip.pypa.io/en/latest/reference/pip_install.html#git

#pip install git+https://github.com/django/django.git@1.7b3