The objective of this tutorial is to provide the reader with an easy to follow way of switching between alternative Python versions on Ubuntu 20.04 Focal Fossa Desktop/Server.

In this tutorial you will learn:
  • How to check installed Python versions
  • How to switch between alternative Python versions
How to switch between alternative Python Versions
How to switch between alternative Python Versions

Software Requirements and Conventions Used

Software Requirements and Linux Command Line Conventions
Category Requirements, Conventions or Software Version Used
System Installed Ubuntu 20.04 or upgraded Ubuntu 20.04 Focal Fossa
Software Python2/Python3
Other Privileged access to your Linux system as root or via the sudo command.
Conventions # - requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command
$ - requires given linux commands to be executed as a regular non-privileged user

How to switch between alternative Python Versions step by step instructions

  1. First step is to check what python versions are available on your Ubuntu system. To do so execute the following command:
    $ ls /usr/bin/python*
    /usr/bin/python2  /usr/bin/python2.7  /usr/bin/python3  /usr/bin/python3.7  /usr/bin/python3.7m  /usr/bin/python3.8  /usr/bin/python3-futurize  /usr/bin/python3m  /usr/bin/python3-pasteurize
    
  2. Next, check if you already have some python alternatives configured. To do so run:
    sudo update-alternatives --list python
    update-alternatives: error: no alternatives for python
    
    Currently the system has no python alternatives configured.
  3. In this step we are going to set two Python alternatives, namely it will by Python2 and Python3 alternative. Execute the following commands:
    $ sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 1
    $ sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 2
    

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  5. Confirm that both alternatives are ready to be used:
    $ sudo update-alternatives --list python
    /usr/bin/python2
    /usr/bin/python3
    
  6. Change to alternative python version. For example to change to Python 2 execute the following command:
    $ sudo update-alternatives --config python
    There are 2 choices for the alternative python (providing /usr/bin/python).
    
      Selection    Path              Priority   Status
    ------------------------------------------------------------
    * 0            /usr/bin/python3   2         auto mode
      1            /usr/bin/python2   1         manual mode
      2            /usr/bin/python3   2         manual mode
    
    Press  to keep the current choice[*], or type selection number: 1
    
    Enter selection number. In this case to switch to Python version 2 we enter the 1 selection number.
  7. Check your python version:
    $ python -V
    Python 2.7.17
    
    To switch to Python 3 alternative repeat Step 5 and enter the selection number appropriate to your desired python version.
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