I have installed on Debian Jessie:
Python2.7
Python3.5
I have also installed Jupyter via pip2 and pip3
However when I launch jupyter-notebook I can only use python3 as kernel! How can I switch to pyhton2.7 when using Jupyter?
I tried this with a fresh Debian 8.5 machine on Digital Ocean.
As root, install pip and jupyter from apt, and the development packages, too.
apt-get install python-pip python-dev python3-pip python3-dev libzmq3
pip3 install jupyter
Add the kernel for Python2 using the ipykernel module. The Python3 kernel is installed, already.
pip install ipykernel
python2 -m ipykernel install
When you run jupyter notebook, you should have both Python 2 and Python 3 listed as available kernels. Notice that the Tornado notebook server is serving HTTP on port 8888, which isn't opened by default on many machines. Here is a script that will run Jupyter for you, opening and closing port 8888 and running on a public IP.
I can't test this right now, but jupyter-notebook is probably looking at your $PATH variable to find a python. When you type python --version, is it python2?
If it isn't, you can choose which python to use by changing your $PATH variable so python2 is before python3.
来源：https://stackoverflow.com/questions/34404357/choose-python-kernel-in-jupyter