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In this tutorial you will learn:
  • How to check installed Python versions
  • How to switch between alternative Python versions
Software Requirements and Conventions Used
Category Description
System Requirements, Conventions or Software Version Used
Software Installed Ubuntu 20.04 or upgraded Ubuntu 20.04 Focal Fossa
Other Python2/Python3
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
  4. Confirm that both alternatives are ready to be used:

    $ sudo update-alternatives --list python
  5. 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.

  1. 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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