Python Virtual Environments

This is the least you need to know to get to use a Python virtual environment.

What is a Virtual Environment

At its core, the main purpose of Python virtual environments is to create an isolated environment for Python projects. This means that each project can have its own dependencies, regardless of what dependencies every other project has.

The great thing about this is that there are no limits to the number of environments you can have since they're just directories containing a few scripts.

Pre-requisites

While venv is part of python3, for python2 you need to install virtualenv.

• void-linux: python-virtualenv

Create

To create a new virtual environment:

Python2

mkdir folder
virtualenv folder

If you want to inherit system global packages in your virtual environment use this instead:

mkdir folder
virtualenv --system-site-packages folder

Python3

mkdir folder
python3 -m venv folder

If you want to inherit system global packages in your virtual environment use this instead:

mkdir folder
python3 -m venv --system-site-packages folder

I prefer to use the --system-site-packages option, that way I can have binary modules using the host's package manager. This is in order to avoid having a compiler in the host system.

Activate

To activate a virtual environment:

. <folder>/bin/activate

Pay attention that we are using . to source the script in the current interpreter.

De-Activate

To de-activate:

deactivate

Run from a script

To use the virtual environment from a script (i.e. running as a background daemon) you need to add these to the beginning of your python script:

activate_this = '/path/to/virtualenv/bin/activate_this.py'
execfile(activate_this, dict(__file__=activate_this))

Or from a shell cript:

#!/bin/sh
source name_Env/bin/activate
# virtualenv is now active.
exec python script.py "$@"

References

For more information see:

• Python3 venv
• pipenv & virtual environments
• virtual env primer