Kernels for Python 2 and 3

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

Or using conda, create a Python 2 environment:

conda create -n ipykernel_py2 python=2 ipykernel
source activate ipykernel_py2    # On Windows, remove the word 'source'
python -m ipykernel install --user

If you're running Jupyter on Python 2 and want to set up a Python 3 kernel, follow the same steps, replacing 2 with 3.

The last command installs a :ref:`kernel spec <jupyterclient:kernelspecs>` file for the current python installation. Kernel spec files are JSON files, which can be viewed and changed with a normal text editor.

Kernels for different environments

If you want to have multiple IPython kernels for different virtualenvs or conda environments, you will need to specify unique names for the kernelspecs.

For example, using conda environments:

source activate myenv
python -m ipykernel install --user --name myenv --display-name "Python (myenv)"
source activate other-env
python -m ipykernel install --user --name other-env --display-name "Python (other-env)"

The --name value is used by Jupyter internally. These commands will overwrite any existing kernel with the same name. --display-name is what you see in the notebook menus.

Using virtualenv or conda envs, you can make your IPython kernel in one env available to Jupyter in a different env. To do so, run ipykernel install from the kernel's env, with --prefix pointing to the Jupyter env:

/path/to/kernel/env/bin/python -m ipykernel install --prefix=/path/to/jupyter/env --name 'python-my-env'

Note that this command will create a new configuration for the kernel in one of the prefered location (see jupyter --paths command for more details):

• system-wide (e.g. /usr/local/share),
• in Jupyter's env (sys.prefix/share),
• per-user (~/.local/share or ~/Library/share)

If you want to edit the kernelspec before installing it, you can do so in two steps. First, ask IPython to write its spec to a temporary location:

ipython kernel install --prefix /tmp

edit the files in /tmp/share/jupyter/kernels/python3 to your liking, then when you are ready, tell Jupyter to install it (this will copy the files into a place Jupyter will look):

jupyter kernelspec install /tmp/share/jupyter/kernels/python3