How Do I Add Python3 Kernel to Jupyter (Ipython)

This worked for me on Ubuntu 16.04:

python2 -m pip install ipykernel
python2 -m ipykernel install --user

python3 -m pip install ipykernel
python3 -m ipykernel install --user

Reference to the documentation:
Kernels for Python 2 and 3. Installing the IPython kernel - IPython Docs.

Make sure you have ipykernel installed and use ipython kernel install to drop the kernelspec in the right location for python2. Then ipython3 kernel install for Python3. Now you should be able to chose between the 2 kernels regardless of whether you use jupyter notebook, ipython notebook or ipython3 notebook (the later two are deprecated).

Note that if you want to install for a specific Python executable you can use the following trick:

path/to/python -m ipykernel install <options>

This works when using environments (venv,conda,...) and the <options> let you name your kernel (see --help). So you can do

conda create -n py36-test python=3.6
source activate py36-test
python -m ipykernel install --name py36-test
source deactivate

And now you get a kernel named py36-test in your dropdown menus, along the other ones.

See Using both Python 2.x and Python 3.x in IPython Notebook which has more recent information.

1. Got ipython notebook with Python2 (on Windows7)
2. upgrade to Jupyter with pip install -U jupyter
3. install Python3
4. install Jupyter again using pip3 install jupyter
5. install Python3 kernel using ipython3 kernelspec install-self
6. I finally got 2 working kernels.

for recent versions of jupyter/ipython: use jupyter kernelspec

Full doc:

list current kernels

$ jupyter kernelspec list
Available kernels:
  python2    .../Jupyter/kernels/python2
  python3    .../Jupyter/kernels/python3

In my case, the python3 kernel setup was broken because the py3.5 linked was no longer there, replaced by a py3.6

add/remove kernels

Remove:

$ jupyter kernelspec uninstall python3

Add a new one: Using the Python you wish to add and pointing to the python which runs your jupiter:

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

See more examples in

List again:

$ jupyter kernelspec list
Available kernels:
  python3    /usr/local/lib/python3.6/site-packages/ipykernel/resources
  python2    /Users/stefano/Library/Jupyter/kernels/python2

Doc:

Details

Kernels available are listed under the kernels folder in Jupyter DATA DIRECTORY (see for details).

For instance on macosx that would be /Users/YOURUSERNAME/Library/Jupyter/kernels/

the kernel is simply described by a kernel.json file, eg. for /Users/me/Library/Jupyter/kernels/python3/kernel.json

{
 "argv": [
  "/usr/local/opt/python3/bin/python3.5",
  "-m",
  "ipykernel",
  "-f",
  "{connection_file}"
 ],
 "language": "python",
 "display_name": "Python 3"
}

Rather then manipulating that by hand, you can use the kernelspec command (as above). It was previously available through ipython now through jupyter ( - ).

$ jupyter kernelspec help
Manage Jupyter kernel specifications.

Subcommands
-----------

Subcommands are launched as `jupyter kernelspec cmd [args]`. For information on
using subcommand 'cmd', do: `jupyter kernelspec cmd -h`.

list
    List installed kernel specifications.
install
    Install a kernel specification directory.
uninstall
    Alias for remove
remove
    Remove one or more Jupyter kernelspecs by name.
install-self
    [DEPRECATED] Install the IPython kernel spec directory for this Python.

To see all available configurables, use `--help-all`