So finally I found out how to install Python 3.10 from sources

dependencies needed for building:

sudo apt install -y build-essential libssl-dev libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm libffi-dev zlib1g-dev

Download and extract the sources

cd /opt
sudo wget https://www.python.org/ftp/python/3.10.12/Python-3.10.12.tgz
sudo tar -xvf Python-3.10.12.tgz

Compile and Install

cd Python-3.10.12
sudo ./configure --enable-optimizations
sudo make altinstall

Ubuntu packages all python3 packages separately. By installing python3-pip it also installed the base python3. If you want venv you also have to install it with

sudo apt install python3-virtualenv

Python2 and Python3 have major incompatible differences, but the python3 that ships with Ubuntu will be maintained and you'll get the latest patches with an apt upgrade Ubuntu is stable and updates are generally safe.

I discovered this issue after trying the steps described in this article, which claims support for 20.04 | 22.04 | 23.04.

TL;DR straight to the fix:

echo "deb https://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu/ jammy main" | sudo tee /etc/apt/sources.list.d/deadsnakes-ubuntu-ppa-lunar.list
sudo apt update
sudo apt install python3.12

The journey to get there:

sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update
sudo apt install python3.12

However, as mentioned in the comments above, there is no "lunar" release in their apt ppa, and the apt update command fails. To resolve this, change the contents of /etc/apt/sources.list.d/deadsnakes-ubuntu-ppa-lunar.list (installed by add-apt-repository) from:

deb https://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu/ lunar main
# deb-src https://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu/ lunar main

to

deb https://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu/ jammy main
# deb-src https://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu/ jammy main

This tells apt to install packages for 22.04 ("jammy"), which seems to work just fine on 23.04 for this package.

Then you can just run apt update and apt install python3.12 successfully

First

Never delete or replace the official Python version installed in Ubuntu Linux! It's a mistake of the author of the article you followed, that you can remove unneeded versions of Python after installing Python 3.12. You could never remove the official one. For Ubuntu 22.04 it's 3.10.

In your situation, I don't believe you already deleted the official Python 3.10. You have just removed it from python or python3 alternatives by the update-alternatives program. You can restore APT to a working state again just by running a set of commands like:

• sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.10
• sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.10

Or similar. I hope you will get the docs of update-alternatives and find out the way how to restore your 3.10 Python version in the list of alternatives.

You still can have a few versions installed, along with the official one, and added them all to the alternatives. This will allow your IDEs and other software to see and choose which version to use.

Second

The problem with not installing Python 3.12 fully is because of the incorrectly updated Python package (3.12.1) by the authors of the source repository - deadsnakes. They need to rebuild it with the resolution in order to the core policies which make it unable to be installed (SyntaxError: from __future__ imports must occur at the beginning of the file). I don't see any other ways except the 2 following:

• wait for the resolution by repo authors
• raise this issue with them via official communication ways

As an example, raising this issue can be done on their main issue tracker on GitHub. After they fix the package, you will be able to just run sudo apt update && sudo apt upgrade to get the newest Python 3.12.1 updated fully.