Getting started with venvand pip

Last updated on 2025-04-15 | Edit this page

Overview

Questions

  • How do I create a venv?
  • How do I install packages into my new venv?

Objectives

  • Create a new virtual environment
  • Learn how to activate and deactivate the virtual environment
  • Installing packages in your environment

Introduction

Now we have a grasp of the steps needed to capture the package layer of the computational environment, so let’s get started with venv and pip.

Creating a new Virtual Environment

We can set up a new virtual environment anywhere, but it’s generally considered good practice to set it up in the folder for your project.

So let’s start by creating a directory for our project using the terminal, and the moving into it.

BASH 

mkdir my-new-project
cd my-new-project

Now we can create our virtual environment using the venv module:

BASH 

python -m venv .venv

If we view the contents of the my-new-project directory by using ls (for Windows) or ls -a (for MacOS /Linux), we should see that there is now a .venv sub-directory.

What should I call my virtual environment directory?

You can call the directory that contains the virtual environment whatever you like, but the two conventional names are venv and .venv.

The primary difference between these two is that the . at the start of .venv indicates to MacOS and Linux-based operating systems that this directory should be hidden when you view the parent directory (i.e. my-new-project).

Activating the new virtual environment

Now you’ve created the virtual environment you’re ready to start installing packages, right?

Not quite, the next step is activating the environment. Effectively telling your operating system that it should be using the Python interpreter in your new virtual environment, rather than the one in the base environment. We’ll see why this is important later.

The command you use to do this will depend on the OS you are using:

Once you’ve done this you should see a prompt with name of you environment appear on the left of your console, e.g:

Now you are ready to start installing packages for your project.

Prompt name blues

If you called the directory you created your environment .venv you’ll notice that the name of the environment displayed in your console is the same. This isn’t very informative, especially if you’re switching between multiple projects (are you sure you’re installing that package in the right .venv?)

By defult this name is the same name you gave to the directory contianing the virtual environment, so you could address this by giving the directory a different name e.g.: python -m venv my-new-project-venv, and this will be reflected in the console:

However, this does mean you have to remember the name you gave to the virtual environment for each project. Not the end of the world, but a bit annoying.

--prompt to the rescue

Handily, venv gives you the option to customise the text in the console for each project:

BASH 

python -m venv .venv --prompt my-new-project

Which will set the virtual environment directory name to venv, and the console prompt to my-new-project:

You can even use the name of the current directory without having to type it out:

BASH 

python -m venv .venv --prompt .

Deactivating the current virtual environment

Deactivating the currently activated virtual environment and returning to using the base environment is as simple as using the deactivate command:

BASH 

deactivate

If you want to reactivate the environment then just follow the steps to activate it, no need to create a new one.

Your Turn 1

Create a new project folder, create a new virtual environment inside it, and activate that virtual environment.

Using your Virtual Environment

Now you have a virtual environment set up for your project, let’s start using it.

Installing packages into the Virtual Environment

First let’s reactivate our virtual environment if it’s not already active:

Now we can install packages using pip as we would usually, e.g:

BASH 

python -m pip install emoji

Which will install the latest available version of the emoji package to our environment.

You can check what is installed in your current environment by running:

BASH 

python -m pip list
Package Version
------- -------
emoji   2.14.0
pip     24.2

You can also have a go at importing the package and running the code below:

PYTHON 

import emoji

print(emoji.emojize('Python is :thumbs_up:'))

Your turn 2

Try installing and using a different package (e.g. numpy, pandas, pillow).
Try using python -m pip list when your virtual environment is activated to see if the package is availble in your environment.
What happens if you deactivate you environment and use python -m pip list?

The nuts and bolts of Virtual environments

At this point you may be wondering what is going on behind the scenes to make this all work. So, lets take a brief detour to give you an idea.

Peeking inside .venv

Lets start by looking in the venv directory in your project. The contents will be slightly different depending on your operating system:

So, when you set up the virtual environment venv will (amongst other things):
- create a copy of the Python interpreter (and pip) in the venv directory
- create a place where it can install packages, and
- setup some files that allow the virtual environment to be activated and deactivated

But you now have two Python executables on your computer (at least), how does you computer know which one to use within the virtual environment?

The path to Python

To explain this we need to introduce environmental variables, and specifically the PATH environmental variable.
Environmental variables are values held by your Operating System which tell the Operating System and installed programs how to behave.
One of the more common ones that you may come across is the PATH variable which, in essence, is a is a list of places that your computer will check for executables.
So, when you run Python in the console your computer will go through this list of places, get the location of the Python executables on your system, and then run Python from the first place it finds that executable.

You can see what directories are in your PATH variable by running:

You can also see the locations of a specific executable on the PATH by running:

Challenge

Run the above commands while your virtual environment is activated vs deactivated.
What differences do you see in the PATH variable, and the list of Python locations?

Pulling it together

The parts we’ve looked at in the last 2 sections give us a clearer idea of what Python is doing when you create and activate a virtual environment:

  1. You run python -m venv venv:
    • A directory called venv is created
    • A standard directory structure is created within venv
    • A copy of Python, pip, and the activate/deactivate files are put in a sub-directory of venv (where will depend on your OS)
  2. You activate the virtual environment:
    • The path to venv is added to start of the system’s PATH environmental variable
    • The path to site-packages within venv is added to the PYTHONPATH environmental variable
      • Not disucussed in detail but this is how Python knows where to install/import packages
  3. You deactivate the virtual environment:
    • The path to venv is removed from the start of the system’s PATH environmental variable
    • The path to site-packages within venv is removed from the PYTHONPATH environmental variable

Key Points

  • You can create, activate, and deactivate virtual environments using venv
  • You can installing packages in a virtual environment using pip install, and view installed packages with pip list
  • Python and venv create an directory on your computer that contains your virtual environment ( a seperate Python interpreter and library)
  • Activating and deactivating the virtual environment modifies the PATH and PYTHONPATH environmental variables to add/remove the path to the directory containing the virtual environment.