Beginners beware, this post isn't about overwriting the default python installation, but working with alternative installation of other versions of python on your Ubuntu 20. If you overwrite your default python you are likely to encounter several other issues that may cause you to reinstall your OS, so please go through the complete post and try to make alternate installation.

In this post, I am going to write about a way to install specific python version (python 3.7.5) in your Ubuntu 20 system which initially has Python 3.8. Since, the project I have done till now had the Python version of 3.6 and 3.7. But, after I updated my OS to Ubuntu 20, my virtual environment could not be set upped as per the project requirements.

Because I wanted my old projects to be compatible, first, I thought of way to override my python 3.8 with python 3.7 but had so many other issues.

Now, I have found a way to deal with this version issue, which I will be explaining below.

1 Checking, Initial version of Python that comes with Ubuntu 20

$ python3 --version
Python 3.8.2

2 Installation of pip

a. First updating the packages

$ sudo apt update

b. Installation of pip

# The command below will install all the dependencies required for building Python modules.
$ sudo apt install python3-pip

c. Verification of pip installed

$ pip3 --version
pip 20.0.2 from /usr/lib/python3/dist-packages/pip (python 3.8)

3 Install virtualenv in your local system

Virtualenv is where all the packages required for project will be kept without dealing with local system packages.

$ pip3 install virtualenv

If you want to use Python 3.8 in your project, then, below process can be followed.

# my_project is the project directory
$ mkdir my_project && cd my_project

# Create a virtual environment in your project directory
$ python3 -m virtualenv .venv

# Activating the environment
$ source .venv/bin/activate
$ python --version
Python 3.8.2

But, this isn't our objective, we want to use other python version (Lets say Python 3.7.5). So, for that please see the below steps.

First install specific version of python in your local system without causing conflict in local system

# Update and Upgrades of packages
$ sudo apt update  
$ sudo apt upgrade -y

# Next, install the build tools and Python 3.7 dependencies using the following command:
$ sudo apt install build-essential libssl-dev zlib1g-dev libncurses5-dev libncursesw5-dev libreadline-dev libsqlite3-dev libgdbm-dev libdb5.3-dev libbz2-dev libexpat1-dev liblzma-dev tk-dev libffi-dev

# Next, download the source code of Python 3.7 using the wget tool:
$ cd /tmp
$ wget https://www.python.org/ftp/python/3.7.5/Python-3.7.5.tar.xz

# Next, decompress the tar file using:
$ tar xf Python-3.7.5.tar.xz

# Next, navigate inside your decompressed Python-3.7.0 folder:
$ cd Python-3.7.5

# Build Python 3.7.5 code using the configure and make tools:
$ ./configure --enable-optimizations
$ sudo make -j 8

# Next, run the following command to install the Python 3.7.5:
# Prefer "altinstall" than "install" because install will override the current OS python, and will cause other conflicts in OS.
$ sudo make altinstall


# Python 3.7.5 can run using:
$ python3.7 

After the specific version of python is installed successfully.

Create virtual environment in your project with specific version installed

# First know your specific python version installed path
$ which python3.7
/usr/local/bin/python3.7

# my_project is a project directory
$ mkdir my_project && cd my_project

# Create virtualenv with the specific python version path
$ python3 -m virtualenv --python=/usr/local/bin/python3.7 .venv

# Activating the virtualenv 
$ source .venv/bin/activate

# Test the python path and version
$ which python
my_project/.venv/bin/python

# python --version
Python 3.7.5

Now can work on any project as required.

Would like to get recommendation on this process, or any other ways it can be dealt with.

I am not so familiar with working with server but now i got an almalinux8

  Virtualization: kvm
  Operating System: AlmaLinux 8.10 (Cerulean Leopard)
  CPE OS Name: cpe:/o:almalinux:almalinux:8::baseos
  Kernel: Linux 4.18.0-553.16.1.el8_10.x86_64
  Architecture: x86-64

Next, I need to install python3.9 without changing the default version used by the whole system

python3 --version
Python 3.6.8

and I see

sudo dnf module list | grep -i python
[sudo] password for xxxx:
libselinux-python    2.8             common                                   Python 2 bindings for libselinux
python27             2.7 [d]         common [d]                               Python programming language, version 2.7
python36             3.6 [d][e]      build, common [d]                        Python programming language, version 3.6
python38             3.8 [d]         build, common [d]                        Python programming language, version 3.8
python39             3.9 [d]         build, common [d]                        Python programming language, version 3.9
python38-devel       3.8             build, common                            Python programming language, version 3.8
python39-devel       3.9             build, common                            Python programming language, version 3.9

So my idea is enable, install and modify only my bash

sudo dnf module enable python39
sudo dnf install python39
#open ~/.bashrc
# Add Python 3.9 to PATH
export PATH="/usr/bin/python3.9:$PATH"
alias python=python3.9

Is this the correct way to go? Am I missing something? Thanks and I am sorry for this basic question but I just start my journey to work with server.

I'm Debian 12 Bookworm, the default python version is 3.11. My problem is that it does not support some libraries I want to use yet. So how do I install a specific python version? apt search for python 3.9 returns nothing.