reveal.js

Python Virtual Environments

About Me

I currently work for AnnuityCheck, a Financial Technology company.

Prior to that, I worked for the International Rescue Committee, creating reports for the United Nations (UNHCR) and US State Dept.

What is python virtual environment

A seperate python 'installation' designed to work with an individual project

Simular Ideas in other languages: Node: npm, Ruby: RVM, golang: workspace, java: Maven (or many others).

The concept of Package Management is universal, the implmentation changes by language

Major Advantages

Work on Multiple Projects without fear
Keep packages up to date
Code Sharing

Python applications will often use packages and modules that don’t come as part of the standard library. Applications will sometimes need a specific version of a library, because the application may require that a particular bug has been fixed or the application may be written using an obsolete version of the library’s interface.

This means it may not be possible for one Python installation to meet the requirements of every application. If application A needs version 1.0 of a particular module but application B needs version 2.0, then the requirements are in conflict and installing either version 1.0 or 2.0 will leave one application unable to run.

The solution for this problem is to create a virtual environment, a self-contained directory tree that contains a Python installation for a particular version of Python, plus a number of additional packages.

Different applications can then use different virtual environments. To resolve the earlier example of conflicting requirements, application A can have its own virtual environment with version 1.0 installed while application B has another virtual environment with version 2.0. If application B requires a library be upgraded to version 3.0, this will not affect application A’s environment.

Freeze!

pip freeze > requirements.txt

This is important, anytime you add / remove a package, refreeze

How to Install (windows)

Install Python (exe)

Fix permissions; open powershell as admin and run:

Set-ExecutionPolicy Unrestricted -Force

How to Install (mac)

Install Python (homebrew), and its auto installed!

How to Install (linux)

$ sudo apt install python3

$ sudo apt install python3-venv

Live Demo!

Lets create a virtual env and use it for great good

Win/Mac: python -m venv venv
Linux: python3 -m venv venv

Win: ./venv/Script/activate
Mac/Linux: . venv/bin/activate

All: deactivate

Common Pitfalls

Dont move the virtual env, just recreate

Dont commit the virtual env, be sure to add venv to .gitingore (using a standard .gitignore, it's in there)

Dont delete version numbers from the requirements.txt file