How to Install an Old Version of Python on Debian or Ubuntu

Install Necessary Libs

Update your package manager and install required packages to build python.

sudo apt-get update
sudo apt-get install -y make build-essential libssl-dev zlib1g-dev \
        libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
        libncurses5-dev libncursesw5-dev xz-utils tk-dev libgdbm-dev \
        libc6-dev

Download Python Source Tarball

Say you want to install python 3.7.3, download the source tarball (note that the link is case sensitive).

wget https://www.python.org/ftp/python/3.7.3/Python-3.7.3.tgz

Feel free to browse Python official FTP for other versions.

Build and Install

After downloaded, unzip it and enter the source directory.

tar -zx -f Python-3.7.3.tgz
cd Python-3.7.3

Then start building.

./configure
make
sudo make install

Replace the Symbolic Link

Let's say you already have a python 3.9.2 coming with OS. Before you installed python 3.7.3, python3 --version gives you Python 3.9.2, but after you installed 3.7.3 you will find python3 is referring to python 3.7.3 instead.

Why is that?

In most GNU/Linux systems, there are directory /usr/bin and /usr/local/bin, the former for binaries supplied by OS or package manager, the latter by user. In most systems the latter precedes the former in PATH, which allows users to install alternate versions of binaries to override OS provided ones.

ls -l /usr/bin/python*
lrwxrwxrwx 1 root root       9 Apr  5  2021 /usr/bin/python3 -> python3.9
-rwxr-xr-x 1 root root 5479736 Mar  1  2021 /usr/bin/python3.9

ls -l /usr/local/bin/python*
lrwxrwxrwx 1 root root        9 Jun  3 12:06 /usr/local/bin/python3 -> python3.7
-rwxr-xr-x 2 root root 15329120 Jun  3 12:06 /usr/local/bin/python3.7

Maybe there are some apps in your system relying on python 3.9.2 and you don't want to disrupt them, in which case, you can remove the symbolic link in /usr/local/bin, which is created during installation. Note that you can always explicitly specify which version you want to use by using python3.7 or python3.9 instead of python3.

sudo rm /usr/local/bin/python3

However, if you use command python3 now, you will get an error:

-bash: /usr/local/bin/python3: No such file or directory

That's because BASH doesn't realize the python3 located in /usr/local/bin has been deleted. You need to re-login BASH or let it re-scan PATH.

source ~/.profile
python3 --version
Python 3.9.2