Execute Python script within Jupyter notebook using a specific virtualenv

Here’s what worked for me (non conda python):
(MacOS, brew version of python. if you are working with system python, you may (will) need prepend each command with sudo)

1. First activate virtualenv. If starting afresh then, e.g., you could use virtualenvwrapper:

   $ pip install virtualenvwrapper
   $ mkvirtualenv -p python2 py2env 
   $ workon py2env
   
   # This will activate virtualenv
   
   (py2env)$ 
   
   # Then install jupyter within the active virtualenv
   (py2env)$ pip install jupyter
   
   # jupyter comes with ipykernel, but somehow you manage to get an error due to ipykernel, then for reference ipykernel package can be installed using:
   (py2env)$ pip install ipykernel
   

2. Next, set up the kernel

   (py2env)$ python -m ipykernel install --user --name py2env --display-name "Python2 (py2env)"
   

3. then start jupyter notebook (the venv need not be activated for this step)

   (py2env)$ jupyter notebook
   # or
   #$ jupyter notebook
   

In the jupyter notebook dropdown menu: Kernel >> Change Kernel >> <list of kernels> you should see Python2 (py2env) kernel.

This also makes it easy to identify python version of kernel, and maintain either side by side.

Here is the link to detailed docs:
http://ipython.readthedocs.io/en/stable/install/kernel_install.html