Type following in the terminal (Ctrl+Alt+T):

python -V

or

python --version

You can find a list of options/parameters for many commands in the terminal by typing the command followed by --help

Example:

python --help

Manual/manpages also available for most of such CLI which can be displayed by man <command> (Ex: man python)

From man python:

COMMAND LINE OPTIONS
        -V ,  --version
              Prints the Python version number of the executable and exits.

There is also python3 installed on many machines, so you can do:

python3 --version

to find out what python 3.x you are running.

we can directly use this to see all the pythons installed both by current user and the root by the following: whereis python

pyenv

https://github.com/pyenv/pyenv

Pyenv allows you to manage multiple Python versions without sudo for a single user, much like Node.js NVM and Ruby RVM.

Install Pyenv:

curl https://pyenv.run | bash

Then add to your .bashrc:

export PATH="${HOME}/.pyenv/bin:$PATH"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"

Find Python version to install:

pyenv install --list

Install the python version you want:

# Increase the chances that the build will have all dependencies.
# https://github.com/pyenv/pyenv/wiki/Common-build-problems
sudo apt build-dep python3
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 libffi-dev liblzma-dev python-openssl git

# Build and install a Python version from source.
pyenv install 3.8.0

List available Python versions:

pyenv versions

We now have:

* system (set by /home/cirsan01/.pyenv/version)
  3.8.0

Select a different python version for the current shell session:

pyenv global 3.8.0
python --version
python3 --version

Both output:

Python 3.8.0

We can now proceed to install and use packages normally:

pip install cowsay
python -c 'import cowsay; cowsay.tux("Python is fun")'
cowsay 'hello'

We can confirm that everything is locally installed in our clean environemnt with:

python -c 'import cowsay; print(cowsay.__file__)'
which cowsay

Per project usage

In the previous section, we saw how to use pyenv in a global setup.

However, what you usually want is to set a specific python and package version on a per-project basis. This is how to do it.

First install your desired Python version as before.

Then, from inside your project directory, set the desired python version with:

pyenv local 3.8.0

which creates a file .python-version containing the version string.

And now let's install a package locally just for our project: TODO: there is no nice way it seems: https://stackoverflow.com/questions/30407446/pyenv-choose-virtualenv-directory/59267972#59267972

Now, when someone wants to use your project, they will do:

pyenv local

which sets the Python version to the correct one.

Tested on Ubuntu 18.04, pyenv 1.2.15.

Conda

I'm not a huge fan of conda's bloatedness, but for better or worse it has become a popular way to manage Python versions and prebuilt shared libraries.

Install miniconda on Linux with:

mkdir -p ~/miniconda3
wget https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh -O ~/miniconda3/miniconda.sh
bash ~/miniconda3/miniconda.sh -b -u -p ~/miniconda3
rm ~/miniconda3/miniconda.sh

and add this to your .bashrc:

PATH="$PATH:$HOME/miniconda3/bin"

then to create a new environment for a project with a specific Python version:

conda create -y -n mytest3.9 python=3.9

and then for each shell where you want to use it in:

eval "$(command conda 'shell.bash' 'hook' 2> /dev/null)"
conda activate mytest3.9

then:

python --version

gives:

Python 3.9.21

and:

which python

gives:

/home/ciro/miniconda3/envs/mytest3.9/bin/python

It also ships its own pip:

which pip

giving:

/home/ciro/miniconda3/envs/mytest3.9/bin/pip

from which you can pip install as in a virtualenv.

You can also let conda modify your .bashrc automatically for you with:

conda init

but unfortunately the code it adds automatically puts you into Conda on every shell which I don't like, so I prefer to do the eval manually per shell as mentioned at: https://stackoverflow.com/questions/55507519/python-activate-conda-env-through-shell-script

Tested on conda 25.1.1, Ubuntu 24.10.

Related threads

• https://askubuntu.com/questions/682869/how-do-i-install-a-different-python-version-using-apt-get
• https://stackoverflow.com/questions/10960805/apt-get-install-for-different-python-versions/59268046#59268046