Switching Kernels: Using Python 2.7 and Python 3.5 in Jupyter Notebooks

Jupyter Notebooks are a great way for working with Python interactively. The integration of Python code into documents is very useful for reports or for writing executable documentation of algorithms and functions. The text can be structured and exported in various formats. With the ever increasing popularity of Python based on the data science hype, more and more libraries are available. Although Python3 is considered to be the future of Python, consensus on the question Python 2.7 vs Python 3.5 is not yet reached. There are quite a few differences and Python 3 is not backwards compatible and therefore the code cannot be executed with both versions without modification. When you install Jupyter Notebooks via Anaconda, Python3 is recommended but Python 2.7 packages also exist.

As there is a large number of libraries, which have not yet been ported to Python 3, it can be useful to switch between the language version within a Jupyter Notebook. The following example assumes that you have both Python versions already installed.

Installing a new Kernel

In Jupyter Notebooks, the kernel is responsible for executing Python code. When you install the Anaconda System for Python3, this version also becomes the default for the notebooks. In order to enable Python 2.7 in your notebooks, you need to install a new kernel like this:

sudo python2 -m pip install --upgrade ipykernel
sudo python2 -m ipykernel install

Restart Jupyter to activate the new Python 2.7 kernel.

Switching Kernels

After restarting Jupyter, you can select the kernel and thereby which version to run the code easily from the menu:



3 thoughts on “Switching Kernels: Using Python 2.7 and Python 3.5 in Jupyter Notebooks

  1. Hi,
    Thanks a lot. I was actually searching for any ‘sudo’ command for installing the python2 kernel, none worked but this one did.
    Thanks once again.
    Best Wishes.

  2. Try the same thing in windows
    py -m pip install –upgrade ipykernel
    py -m ipykernel install

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