venv.md

Virtual environment / virtualenv / venv / env

Virtualenv is a tool to create isolated Python environments. (if you want to learn more about it go there).

This tool will allow us to create a virtual environment for each project. Each project can install its own dependencies without contaminating other projects.

This also means that you will be able to share your project with a liste of every dependencies required, easily via a file called requirements.txt (more on this later).

Usage

First we need to create the venv :

# python3 -m venv <name_of_venv>
# usually we name it venv
python3 -m venv venv
# creates a venv directory which contains the virtualenvironment

Then we need to activate it :

# macos and linux
source venv/bin/activate
# windows
source venv/Scripts/Activate.ps1

Note : some code editor like pycharm or vscode will automatically detect virtualenvironments.

Depending on your shell (zsh for example) you can have a visual indicator telling you that you're in a venv.

# example
(venv) $ ...

We can now install dependencies in our venv :

(venv) $ pip install flask
Collecting flask
  Using cached Flask-2.0.2-py3-none-any.whl (95 kB)
Collecting Jinja2>=3.0
  Using cached Jinja2-3.0.3-py3-none-any.whl (133 kB)
Collecting Werkzeug>=2.0
  Using cached Werkzeug-2.0.2-py3-none-any.whl (288 kB)
Collecting click>=7.1.2
  Using cached click-8.0.3-py3-none-any.whl (97 kB)
Collecting itsdangerous>=2.0
  Using cached itsdangerous-2.0.1-py3-none-any.whl (18 kB)
Collecting MarkupSafe>=2.0
  Using cached MarkupSafe-2.0.1-cp39-cp39-macosx_10_9_x86_64.whl (13 kB)
Installing collected packages: MarkupSafe, Werkzeug, Jinja2, itsdangerous, click, flask
Successfully installed Jinja2-3.0.3 MarkupSafe-2.0.1 Werkzeug-2.0.2 click-8.0.3 flask-2.0.2 itsdangerous-2.0.1

flask is now installed only in this venv, not globally. yay

To verify this, open a new terminal, don't activate the venv, and try to call flask. You should have an error. (of course, except if you installed flask earlier as a global dependency...)

Let's move forward in time and imagine that we developed a nice app. We want to share the list of dependencies required to dev/run/test the app. To export this list we use the command freeze :

(venv) $ pip3 freeze
click==8.0.3
Flask==2.0.2
itsdangerous==2.0.1
Jinja2==3.0.3
MarkupSafe==2.0.1
Werkzeug==2.0.2

Here we can see that by installing only flask, it pulled a lot of other dependencies with it.

To version this file and share it, we redirect the command to a file named requirements.txt :

(venv) $ pip3 freeze > requirements.txt

Here's an example of a real project : https://github.com/kellyjonbrazil/jc/blob/master/requirements.txt

This file, requirements.txt will be committed alongside your source code. But you must not commit the venv folder. So make sure to add it in the .gitignore file of your project.

Also make sure to update your requirements.txt every time you update/install a dependency. 🙃

Note : you can read a complete gitignore file here > https://www.toptal.com/developers/gitignore/api/python

To quit the venv :

``bash (venv) $ deactivate