Virtual Environments (venv)

Introduction

Imagine two different projects on your computer: one needs version 1.0 of a library, and another needs version 3.0 of the exact same library. If Python only had one global place to install packages, you would not be able to satisfy both projects at the same time. Virtual environments solve exactly this problem.

In this lesson, you will learn why virtual environments matter, how to create and activate one using Python's built-in venv module, how to tell when one is active, and why professional Python projects almost always use them.

Why Virtual Environments Exist

Every Python installation has one global set of installed packages by default. If every project shared that same global set, you would quickly run into conflicts: Project A needs requests version 2.10, Project B needs requests version 2.31, and installing one would break the other.

A virtual environment (often shortened to "venv") is an isolated, self-contained folder that holds its own Python interpreter copy and its own separate set of installed packages, completely independent from your system's global Python installation and from any other project's virtual environment.

Creating a Virtual Environment

Python includes a built-in module called venv specifically for creating virtual environments — no separate installation needed. Run this command inside your project folder.

python -m venv venv

Here, python -m venv runs the venv module, and the second venv is simply the name of the folder that will be created to hold the environment. You can name it anything, but venv (or .venv) is the most common convention.

my_project/
    venv/
        Scripts/
        Lib/
        pyvenv.cfg
    main.py

my_project/
    venv/
        bin/
        lib/
        pyvenv.cfg
    main.py

Activating a Virtual Environment

Creating a venv does not automatically use it — you must activate it first. The activation command differs depending on your operating system and shell.

venv\Scripts\activate

source venv/bin/activate

How to Tell a venv is Active

Once activated, your terminal prompt changes to show the environment's name in parentheses at the start of the line. This is the quickest visual confirmation that the virtual environment is active.

C:\my_project>

(venv) C:\my_project>

You can also confirm which Python interpreter is currently in use — it should now point inside the venv folder rather than your system Python.

which python

/home/user/my_project/venv/bin/python

Deactivating a Virtual Environment

When you are done working, or want to switch back to the global Python installation, simply run the deactivate command — it works the same way on every operating system.

deactivate

The (venv) prefix disappears from your prompt, confirming you are back to using the system-wide Python environment.

Why Not Install Globally?

It can feel like an extra, unnecessary step to create and activate a venv for every project — but skipping it causes real problems as soon as you work on more than one project.

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Virtual environments keep each Python project's dependencies isolated, avoiding version conflicts and keeping your global Python installation clean. Creating one is a single command, and activating it is just as simple, though the exact command depends on your operating system.

With a solid understanding of why and how to use venv, you are ready to learn how to actually install and manage packages inside that environment using pip, in the next lesson.