How to change default Python version

Checking your current Python version

To check your current Python version, run:

python3 --version

Alternatively, you can run:

python --version

In most instances, python maps to a Python 2.X installation and python3 maps to a Python 3.X version (as the name implies).

Changing your default python3 version

To see the Python 3.X versions you have installed, run the following command:

ls /usr/bin/python3*

We can use update-alternatives to change python3 to run our desired version.

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 2

The number at the end of each line is the priority number. We can change the order of the priority through following the instructions after running:

sudo update-alternatives --config python3

Changing your default python version

Similarly, we will use update-alternatives to change what python runs. We can run the following command to see all of our Python installations:

ls /usr/bin/python*

We can follow a similar process as before by assigning Python versions different priorities.

sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.6 2

Note: It is highly recommended that you keep python pointing to a Python 2.X version rather than a 3.X version. Some operating systems rely on python being a Python 2.X version and may break otherwise.