Virtual Environments & Packages

Notes from Chapter 12 of the Python 3 official tutorial, Virtual Environments & Packages.

A virtual environment is a self-contained directory tree that contains an installation of a particular version of Python, plus additional packages.
venv is the module used to create & maintain virtual environments. It is included in the standard library for Python 3.3+.
Command in terminal to create new venv is python3 -m venv \[new directory name].’ Here python3 -m means run the venv module as a script. The new venv is created with the default version of python3.
Need to activate the venv before using it. For MacOS, the command is source \[directory-name]/bin/activate.
Command to deactivate venv is deactivate.
Use pip to install desired packages into venv.
(To list all packages in current venv, command is pip list.)
(To see more info about a package, command is pip show.)
Use pip freeze command in creating requirements.txt file.
To install all requirements for an application, use the app’s requirements.txt file and and run pip install -r requirements.txt

Venvs are important for giving each project its own space where it can have all its dependencies (in appropriate versions), without running into potential conflicts among projects.
The most important tools for working with venvs are is the venv module (for creating them) and pip for adding additional packages, etc.