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Python

Updated June 17, 2025

Create a virtual environment

brew and admin rights required

To use the instructions below, you absolutely need admin rights AND brew installed.

For the latter you can follow the instructions here. For the former, you need to request your manager/supervisor to petition for those rights for valid reasons. Once you have approval, contact the IT manager to switch your account.

If you see an error message when trying to run python3 or pip command that says this:

Error: externally-managed-environment

... then three options are available to you:

✅ Best method

Run this command to create a virtual environment:

python3 -m venv venv
... then activate it: 
source venv/bin/activate
Use Python as usual. Once you're done, issue this command to deactivate it: 
deactivate

🙂 Most convenient

See below, Managing multiple Local Python Versions

👎 Discouraged

Alternatively, but not reccommended as it is less safe, you need to add this flag:

--break-system-packages
... to every Python and Pip commands to silence this message.

Managing multiple Local Python Versions

Working with multiple Python projects can be overwhelming, especially when switching from one Python runtime version to another. A good way to achieve a proper switch without breaking the ability to execute conflicting projects is to use Python environments.

Important

pyenv is unaware of any Python installations it didn’t install itself. Therefore it is recommended to start with an environment where no version of Python is installed but the default OS Python installation.

Install pyenv on macOS

brew and admin rights required

To use the instructions below, you absolutely need admin rights AND brew installed.

For the latter you can follow the instructions here. For the former, you need to request your manager/supervisor to petition for those rights for valid reasons. Once you have approval, contact the IT manager to switch your account.

Install dependencies

xcode-select --install

brew update && brew upgrade

brew install openssl readline sqlite3 xz zlib tcl-tk@8 libb2

Instal pyenv via brew

brew update && brew install pyenv

Note

No Python version is installed with pyenv, you need to install one manually.

See Install a specific version of Python or Install the most recent Python 3 version below.

Set up your shell environment for pyenv

source ~/.zshrc
Then add this, save and exit: 
echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.zshrc
echo '[[ -d $PYENV_ROOT/bin ]] && export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.zshrc
echo 'eval "$(pyenv init - zsh)"' >> ~/.zshrc

Install pyenv-virtualenv on macOS

brew and admin rights required

To use the instructions below, you absolutely need admin rights AND brew installed.

For the latter you can follow the instructions here. For the former, you need to request your manager/supervisor to petition for those rights for valid reasons. Once you have approval, contact the IT manager to switch your account.

Next, install pyenv-virtualenv: 

brew install pyenv-virtualenv
... and then check the list of installed versions: 
pyenv versions

Set up your shell environment for pyenv

source ~/.zshrc
Then add this, save and exit: 
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
Then: 
source ~/.zshrc

Check which virtual environments are installed

pyenv virtualenvs

Install a Python version

Install the target version you want if it’s not in the list, exemple: 

pyenv install 3.10.5

Or install the target Python version in a virtual environment: 

pyenv virtualenv 3.10.5 venv310
... and activate the environment: 
pyenv activate venv310

Then restart your shell for the PATH changes to take effect, or: 

source ~/.zshrc

Uninstall a virtual environment

pyenv uninstall venv310
You’ll get a confirmation prompt, press Y to confirm.

Useful commands

List available versions

pyenv install -l

Install the most recent Python 3 version

pyenv install 3

or... 

pyenv install 3.10
... will install the most recent version which is 3.10.16

Install a specific version of Python

pyenv install 3.10.4

Switch between Python versions

To select a pyenv-installed Python as the version to use, run one of the following commands:

More information

https://github.com/pyenv/pyenv#how-it-works

Install Python 3 on Debian/Ubuntu

Install dependencies

sudo apt install software-properties-common build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev wget

Install the latest version...

sudo apt install python3 -y

...or install a specific version.

sudo apt install python3.12 -y

Install the virtual environment plug-in

apt install python3-virtualenv -y
apt install python3.12-venv

Install pip

apt install python3-pip -y
Check everything is installed properly: 
python3 --version