How can I change the default python on my Ubuntu 20.04 to Python3.8?

I would like to set python 3.8 as default on my PC Thinkpad X230 Ubuntu 20.04

I tried setting an alias

gt@gt-ThinkPad-X230:~$ alias python='usr/bin/python3.8'

Q: Does this alter a .bashrc file? If so, which? ~/.bashrc? another? if so, which?

gt@gt-ThinkPad-X230:~$ python --version
bash: usr/bin/python3.8: No such file or directory

Complains it cannot find /usr/bin/python3.8, buuuuut:

gt@gt-ThinkPad-X230:~$ ls /usr/bin/python*

/usr/bin/python /usr/bin/python3.8 /usr/bin/python3-pasteurize /usr/bin/python2 /usr/bin/python3.8-config /usr/bin/python3-unidiff /usr/bin/python2.7 /usr/bin/python3-config /usr/bin/python3 /usr/bin/python3-futurize

How do I get bash to find see /usr/bin/python3.8?

The correct way is sudo apt install python-is-python3 - it effectively does a symlink, but it also keeps pace with future updates; so if your ubuntu distribution moves to say Python 3.9, the manual symlink will no longer work, but the package makes sure it is still valid.

Firstly to answer your question, your approach should work, I think the path you've given in your alias needs the / preceding the path so the command should be alias python='/usr/bin/python3.8', this would indeed need to go into your ~/.bashrc file assuming you are using bash.

Secondly, Ubuntu has a really nice method of setting default binaries globally rather than messing with dot config files as depicted here: update-alternatives

a better solution may be to simply run:

sudo update-alternatives  --set python /usr/bin/python3.8

This will ensure you have the version of python in use that you intend, everywhere.