How to Set Default Python Version to Python3 in Ubuntu

Unable to set default python version to python3 in ubuntu

EDIT:

I wrote this when I was young and naive, update-alternatives is the better way to do this. See @Pardhu's answer.

Outdated answer:

Open your .bashrc file nano ~/.bashrc. Type alias python=python3
on to a new line at the top of the file then save the file with ctrl+o
and close the file with ctrl+x. Then, back at your command line type
source ~/.bashrc. Now your alias should be permanent.

How to set default python3 to python 3.9 instead of python 3.8 in Ubuntu 20.04 LTS

You should be able to use python3.9 -m pip install <package> to run pip with a specific python version, in this case 3.9.

The full docs on this are here: https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/

If you want python3 to point to python3.9 you could use the quick and dirty.

alias python3=python3.9

EDIT:

Tried to recreate your problem,

# which python3
/usr/bin/python3
# python3 --version
Python 3.8.10
# which python3.8
/usr/bin/python3.8
# which python3.9
/usr/bin/python3.9

Then update the alternatives, and set new priority:

# sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.9 1
# sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.9 2
# sudo update-alternatives --config python3
There are 2 choices for the alternative python3 (providing /usr/bin/python3).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /usr/bin/python3.9   2         auto mode
  1            /usr/bin/python3.8   2         manual mode
* 2            /usr/bin/python3.9   2         manual mode

Press <enter> to keep the current choice[*], or type selection number: 0

Check new version:

# ls -alith /usr/bin/python3
3338 lrwxrwxrwx 1 root root 25 Feb  8 14:33 /usr/bin/python3 -> /etc/alternatives/python3
# python3 -V
Python 3.9.5
# ls -alith /usr/bin/pip3
48482 -rwxr-xr-x 1 root root 367 Jul 13  2021 /usr/bin/pip3
# pip3 -V
pip 20.0.2 from /usr/lib/python3/dist-packages/pip (python 3.9)

Hope this helps (tried it in wsl2 Ubuntu 20.04 LTS)

Permanently change the default Python3 version in Linux (Ubuntu on Windows)

You can always use
sudo update-alternatives --config python3
and then select your python3 version.
That should solve your issue without needing to do weird configs.

How do I change my default python 3 having more than one version installed (Ubuntu 18.04)?

The python and python3 commands are usually soft links to the actual executables and you can change the targets. For example:

Firstly, find out where python 3.6 and python 3.8 are located:

# which python
/usr/bin/python
# ls -l /usr/bin/python
/usr/bin/python -> python3.8
# which python3
/usr/bin/python3
# ls -l /usr/bin/python3
/usr/bin/python3 -> python3.6

Then, change the soft links:

# rm /usr/bin/python3
# ln -s /usr/bin/python3.8 /usr/bin/python3

how to make virtualenv see the default python version on Ubuntu

You can use the below command for ensuring that virtualenv refers to python3.8 by default

python3.8 -m virtualenv myenv