Setting up your environment

Python

Python is a scripting language, which is available on a number of different operating systems. However, depending on what system you are using, your version of Python is going to be different. Because of this reason, we specify exactly which version of Python we expect the code to work with.

For the following instructions, we're going to assume that you know exactly which version of Python you need to install. Normally, this is listed in the README.md file or in the tutorial information. Our CI systems have to be told exactly which version of Python is required, too. So if you're really stuck, try looking at the .github/workflows/ci.yml file for the specific version you need.

$ cd /path/to/your/project
$ pyenv install 3.12.1
$ pyenv local 3.12.1

Virtual Environments

When Python is installed, it provides a single global environment. By default, if you install a package, it will be installed into this global environment.

However, if you're working on more than one Python project, it's entirely likely that those multiple projects will have different - and in some cases, conflicting - requirements. What you need is a way to isolate each project so that installing a package for one project won't force that same package to be installed for the second project.

This is done using Virtual Environments. A Virtual Environment, or venv, is an isolated environment that can be easily created, destroyed or recreated. Any package installed in the virtual environment is only accessible inside that virtual environment. Virtual environments are sometimes referred to as a "sandbox" - a safe place to play, where if you make a mistake, you can knock down everything you've built and start again.

Python provides the venv module to create new virtual environments. Each virtual environment has a name that can be used to identify the environment. To create a fresh virtual environment named "my-venv", run:

$ python -m venv my-venv

The version of Python that you use to create the virtual environment will be the version that is used by default inside the virtual environment. If you've got multiple Python versions installed, or you're using a tool like pyenv to manage Python versions, ensure that the Python version that is currently active (or the version you reference when invoking the -m venv command) is the version you intend. Once a virtual environment has been created, you can't change the Python version that it is using. To change the Python version, you need to create a fresh virtual environment.

Invoking -m venv will create the virtual environment, but the environment is not yet active. The virtual environment is a collection of files on disk, stored in a directory that matches the name of the environment. To activate the virtual environment, you run one of the files generated as part of the environment:

$ source my-venv/bin/activate

This will result in a prefix being added to your command line prompt letting you know you're in a virtual environment:

(my-venv) $

While the virtual environment is active, any pip install command will only affect the virtual environment. It doesn't matter if you change directories - if your prompt has a prefix, that virtual environment is active.

If you open a second terminal window, the environment will not be active - you need to re-activate the environment in every terminal session where you want to use the environment. If you get errors about libraries not being available that you're certain you've installed - check whether your virtual environment is active.

To deactivate the virtual environment, run:

(my-venv) $ deactivate

Once deactivated, the prefix will be dropped from the prompt.