13.3. Module venv

  • Isolated Python environment

  • Allows to have multiple versions of Python for one project

  • For testing on different versions: python3.11, python3.12, python3.13

  • Test libraries and frameworks before upgrading (create venv, install requirements, run tests, delete if fails)

  • Allows to have different versions of libraries and frameworks for each project

  • Difference between venv and virtualenv

  • venv is bundled with Python since 3.3 (no installation required)

  • virtualenv is independent package installed via pip

  • virtualenvwrapper is additionally installed command line tools

13.3.1. Venv vs Virtualenv

Both venv and virtualenv are used to create isolated Python environments. Since Python 3.3, a subset of virtualenv has been integrated into the standard library under the venv module.

Both venv and virtualenv:

  • Author: Bernat Gabor

  • Support: Python 3

Module venv:

  • Python: version 3 only

  • Install: not required - bundled with Python since Python 3.3

  • Usage: python3.12 -m venv DIRECTORY

  • Development: synchronized with Python releases

  • Features: all you need

Module virtualenv:

  • Python: version 2 and 3

  • Install: pip install virtualenv

  • Usage: virtualenv DIRECTORY

  • Development: independent from Python releases

  • Features: all from venv plus extra (which typically you don't need)

In my opinion builtin venv is all you need. Moreover no installation is required to use it.

13.3.2. Create

  • venv-py312 is the name of venv folder

  • See "Directory Naming Convention" below

Create virtual environment in directory named venv-py312:

$ python3.12 -m venv venv-py312

13.3.3. Run Ad-Hoc

  • Will run python with from virtual environment

  • With all the modules already installed

Run myscript.py using virtual environment:

$ venv-py312/bin/python3 myscript.py

13.3.4. Activate

  • bin for macOS, Linux, BSD

  • Scripts for Windows

  • Note the direction of slash and backslash (OS dependent)

There is a slight difference between activating virtual environment on macOS, Linux, BSD and Windows.

Linux, macOS, BSD:

$ source venv-py312/bin/activate


$ venv-py312\Scripts\activate.bat

13.3.5. Install Modules Ad-Hoc

Install new module:

$ venv-py312/bin/python -m pip install MODULE

Install modules listed in requirements.txt

$ venv-py312/bin/python -m pip install -r requirements.txt

Upgrade modules listed in requirements.txt:

$ venv-py312/bin/python -m pip install --upgrade -r requirements.txt

List installed modules:

$ venv-py312/bin/python -m pip freeze

13.3.6. Directory Naming Convention

  • No standard naming convention

  • Naming directory like module (venv) name is a good idea

  • Adding Python version is also a good practice

  • Optionally naming per main framework/library version

  • Dot at the beginning hides directory on Linux and macOS (but doesn't work on Windows)

  • Underscore is Python convention for private/protected, but does not work for OS and Git

venv  # may be confused with ``venv`` Python module, mind: ``sys.path``

13.3.7. Good Practices

  • python3.12 -m venv -h

  • python3.12 -m venv --upgrade-deps venv-py312

  • Name venv directory similar to python version venv-py3.12

  • Place in your project directory

  • Add venv directory to .gitignore (important!)

  • Change prompt by appending at the end of venv-3.12/bin/activate:

13.3.8. Bash Prompt

  • Default on most Linux distributions

  • \e[ – This string tells bash prompt to apply color from next character.

  • 0;32m – This string represents the colors. The number before the; represent typeface. And the number after the ; represent color code.

  • \e[0m – This string will tell the bash prompt to apply the color to the previous character.


  • 0 – Normal

  • 1 – Bold

  • 2 – Dim

  • 4 – Underlined

Color codes:

  • 30 – Black

  • 31 – Red

  • 32 – Green

  • 33 – Brown

  • 34 – Blue

  • 35 – Purple

  • 36 – Cyan

  • 37 – Light gray

Define variables for Bash colors:


Set Bash prompt:

export PS1="\n${cyan}myproject> ${white}"

13.3.9. Zsh Prompt

  • Default on macOS

  • Colors: black, blue, cyan, green, magenta, red, white, yellow

export PROMPT="%F{cyan}myproject> %F{white}"

Optionally you can also set options:

setopt PROMPT_CR
setopt PROMPT_SP

13.3.10. Further Reading

13.3.11. Assignments

Code 13.13. Solution
* Assignment: Virtualenv
* Complexity: easy
* Lines of code: 0 lines
* Time: 2 min

    1. Create `venv` for newest Python version
    2. Add `venv` as a Python interpreter in your IDE
    3. Run doctests - all must succeed

    1. Stwórz `venv` dla najnowszej wersji Python
    2. Dodaj `venv` jako interpreter Python w Twoim IDE
    3. Uruchom doctesty - wszystkie muszą się powieść