Using both Python 2.x and Python 3.x in IPython Notebook


I use IPython notebooks and would like to be able to select to create a 2.x or 3.x python notebook in IPython.

I initially had Anaconda. With Anaconda a global environment variable had to be changed to select what version of python you want and then IPython could be started. This is not what I was looking for so I uninstalled Anaconda and now have set up my own installation using MacPorts and PiP. It seems that I still have to use

port select --set python <python version> 

to toggle between python 2.x and 3.x. which is no better than the anaconda solution.

Is there a way to select what version of python you want to use after you start an IPython notebook, preferably with my current MacPorts build?

10/9/2015 6:24:08 PM

Accepted Answer

A solution is available that allows me to keep my MacPorts installation by configuring the Ipython kernelspec.


  • MacPorts is installed in the usual /opt directory
  • python 2.7 is installed through macports
  • python 3.4 is installed through macports
  • Ipython is installed for python 2.7
  • Ipython is installed for python 3.4

For python 2.x:

$ cd /opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin
$ sudo ./ipython kernelspec install-self

For python 3.x:

$ cd /opt/local/Library/Frameworks/Python.framework/Versions/3.4/bin
$ sudo ./ipython kernelspec install-self

Now you can open an Ipython notebook and then choose a python 2.x or a python 3.x notebook.

Choose your python!

8/27/2015 6:08:14 PM

If you’re running Jupyter on Python 3, you can set up a Python 2 kernel like this:

python2 -m pip install ipykernel

python2 -m ipykernel install --user


These instructions explain how to install a python2 and python3 kernel in separate virtual environments for non-anaconda users. If you are using anaconda, please find my other answer for a solution directly tailored to anaconda.

I assume that you already have jupyter notebook installed.

First make sure that you have a python2 and a python3 interpreter with pip available.

On ubuntu you would install these by:

sudo apt-get install python-dev python3-dev python-pip python3-pip

Next prepare and register the kernel environments

python -m pip install virtualenv --user

# configure python2 kernel
python -m virtualenv -p python2 ~/py2_kernel
source ~/py2_kernel/bin/activate
python -m pip install ipykernel
ipython kernel install --name py2 --user

# configure python3 kernel
python -m virtualenv -p python3 ~/py3_kernel
source ~/py3_kernel/bin/activate
python -m pip install ipykernel
ipython kernel install --name py3 --user

To make things easier, you may want to add shell aliases for the activation command to your shell config file. Depending on the system and shell you use, this can be e.g. ~/.bashrc, ~/.bash_profile or ~/.zshrc

alias kernel2='source ~/py2_kernel/bin/activate'
alias kernel3='source ~/py3_kernel/bin/activate'

After restarting your shell, you can now install new packages after activating the environment you want to use.

python -m pip install <pkg-name>


python -m pip install <pkg-name>

With a current version of the Notebook/Jupyter, you can create a Python3 kernel. After starting a new notebook application from the command line with Python 2 you should see an entry „Python 3“ in the dropdown menu „New“. This gives you a notebook that uses Python 3. So you can have two notebooks side-by-side with different Python versions.

The Details

  1. Create this directory: mkdir -p ~/.ipython/kernels/python3
  2. Create this file ~/.ipython/kernels/python3/kernel.json with this content:

        "display_name": "IPython (Python 3)", 
        "language": "python", 
        "argv": [
            "-c", "from IPython.kernel.zmq.kernelapp import main; main()", 
            "-f", "{connection_file}"
        "codemirror_mode": {
            "version": 2, 
            "name": "ipython"
  3. Restart the notebook server.

  4. Select „Python 3“ from the dropdown menu „New“
  5. Work with a Python 3 Notebook
  6. Select „Python 2“ from the dropdown menu „New“
  7. Work with a Python 2 Notebook

From my Linux installation I did:

sudo ipython2 kernelspec install-self

And now my python 2 is back on the list.



The method above is now deprecated and will be dropped in the future. The new method should be:

sudo ipython2 kernel install


Following are the steps to add the python2 kernel to jupyter notebook::

open a terminal and create a new python 2 environment: conda create -n py27 python=2.7

activate the environment: Linux source activate py27 or windows activate py27

install the kernel in the env: conda install notebook ipykernel

install the kernel for outside the env: ipython kernel install --user

close the env: source deactivate

Although a late answer hope someone finds it useful :p