How to switch the default Python version in Debian Linux to an alternative version

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When you install Debian Linux, the installation process may provide you with multiple available Python versions at the same time, so there will be multiple Python executable binaries on the system. You can use the command as follows lsto check which Python binaries are available on your system.

$ ls /usr/bin/python*
/usr/bin/python  /usr/bin/python2  /usr/bin/python2.7  /usr/bin/python3  /usr/bin/python3.4  /usr/bin/python3.4m  /usr/bin/python3m

Execute the following command to view the default Python version information:

$ python --version
Python 2.7.8

1. Modify the Python version based on the user:

aliasTo modify the Python version for a specific user, just create an alias in their home directory . Open the user's ~/.bashrcfile and add new alias information to modify the default Python version.

alias python='/usr/bin/python3.4'

Once the above operation is completed, log in again or reload .bashrcthe file for the operation to take effect.

$ . ~/.bashrc

Check current Python version.

$ python --version
Python 3.4.2

2. Modify the Python version at the system level

We can use update-alternativesto change the Python version for the entire system. Log in as root and first list all available python alternative version information:

# update-alternatives --list python
update-alternatives: error: no alternatives for python

If an error message like the one shown above appears, it means that the alternative version of Python has not been update-alternativesrecognized by the command. To solve this problem, we need to update the substitution list to include python2.7and .python3.4

# update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
update-alternatives: using /usr/bin/python2.7 to provide /usr/bin/python (python) in auto mode
# update-alternatives --install /usr/bin/python python /usr/bin/python3.4 2
update-alternatives: using /usr/bin/python3.4 to provide /usr/bin/python (python) in auto mode

--installOptions take several parameters for creating symbolic links. The last parameter specifies the priority of this option. If we do not set an alternative option manually, the option with the highest priority will be selected. In this example, we /usr/bin/python3.4set the priority to 2, so update-alternativesthe command will automatically set it as the default Python version.

# python --version
Python 3.4.2

Next, we again list the available alternative versions of Python.

# update-alternatives --list python
/usr/bin/python2.7
/usr/bin/python3.4

From now on, we can use the command below to switch between the listed alternative versions of Python at any time.

# update-alternatives --config python

# python --version
Python 2.7.8

3. Remove alternative versions

Once an alternative version of Python no longer exists on our system, we can update-alternativesdelete it from the list. For example, we can remove the python2.7 version from the list.

# update-alternatives --remove python /usr/bin/python2.7
update-alternatives: removing manually selected alternative - switching python to auto mode
update-alternatives: using /usr/bin/python3.4 to provide /usr/bin/python (python) in auto mode

via: http://linuxconfig.org/how-to-change-from-default-to-alternative-python-version-on-debian-linux

Translator: mr-ping Proofreader: wxy

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