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

Question

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?

Answer 1

The idea here is to install multiple ipython kernels. Here are instructions for anaconda. If you are not using anaconda, I recently added instructions using pure virtualenvs.

Anaconda >= 4.1.0

Since version 4.1.0, anaconda includes a special package nb_conda_kernels that detects conda environments with notebook kernels and automatically registers them. This makes using a new python version as easy as creating new conda environments:

conda create -n py27 python=2.7 ipykernel
conda create -n py36 python=3.6 ipykernel

After a restart of jupyter notebook, the new kernels are available over the graphical interface. Please note that new packages have to be explicitly installed into the new environments. The Managing environments section in conda's docs provides further information.

Manually registering kernels

Users who do not want to use nb_conda_kernels or still use older versions of anaconda can use the following steps to manually register ipython kernels.

configure the python2.7 environment:

conda create -n py27 python=2.7
conda activate py27
conda install notebook ipykernel
ipython kernel install --user

configure the python3.6 environment:

conda create -n py36 python=3.6
conda activate py36
conda install notebook ipykernel
ipython kernel install --user

After that you should be able to choose between python2
and python3 when creating a new notebook in the interface.

Additionally you can pass the --name and --display-name options to ipython kernel install if you want to change the names of your kernels. See ipython kernel install --help for more informations.