Python VirtualEnv

What is a Virtual Environment?

A virtual environment in Python is an isolated environment on your computer, where you can run and test your Python projects.

It allows you to manage project-specific dependencies without interfering with other projects or the original Python installation.

Think of a virtual environment as a separate container for each Python project. Each container:

• Has its own Python interpreter
• Has its own set of installed packages
• Is isolated from other virtual environments
• Can have different versions of the same package

Using virtual environments is important because:

• It prevents package version conflicts between projects
• Makes projects more portable and reproducible
• Keeps your system Python installation clean
• Allows testing with different Python versions

Creating a Virtual Environment

Python has the built-in venv module for creating virtual environments.

To create a virtual environment on your computer, open the command prompt, and navigate to the folder where you want to create your project, then type this command:

Example

C:\Users\Your Name> python -m venv myfirstproject

This will set up a virtual environment, and create a folder named "myfirstproject" with subfolders and files, like this:

Result

myfirstproject
  Include
  Lib
  Scripts
  .gitignore
  pyvenv.cfg

Activate Virtual Environment

To use the virtual environment, you have to activate it with this command:

Example

C:\Users\Your Name> myfirstproject\Scripts\activate

After activation, your prompt will change to show that you are now working in the active environment:

Result

(myfirstproject) C:\Users\Your Name>

Install Packages

Once your virtual environment is activated, you can install packages in it, using pip.

We will install a package called 'cowsay':

Example

(myfirstproject) C:\Users\Your Name> pip install cowsay

Result

Collecting cowsay
  Downloading cowsay-6.1-py3-none-any.whl.metadata (5.6 kB)
Downloading cowsay-6.1-py3-none-any.whl (25 kB)
Installing collected packages: cowsay
Successfully installed cowsay-6.1

[notice] A new release of pip is available: 25.0.1 -> 25.1.1
[notice] To update, run: python.exe -m pip install --upgrade pip

Using Package

Now that the 'cowsay' module is installed in your virtual environment, lets use it to display a talking cow.

Create a file called test.py on your computer. You can place it wherever you want, but I will place it in the same location as the myfirstproject folder -not in the folder, but in the same location.

Open the file and insert these three lines in it:

Example

import cowsay

cowsay.cow("Good Mooooorning!")

Then, try to execute the file while you are in the virtual environment:

Example

(myfirstproject) C:\Users\Your Name> python test.py

As a result a cow will appear in you terminal:

Result

  _________________
| Good Mooooorning! |
  =================
                 \
                  \
                    ^__^
                    (oo)\_______
                    (__)\       )\/\
                        ||----w |
                        ||     ||

Deactivate Virtual Environment

To deactivate the virtual environment use this command:

Example

(myfirstproject) C:\Users\Your Name> deactivate

As a result, you are now back in the normal command line interface:

Result

C:\Users\Your Name>

If you try to execute the test.py file outside of the virtual environment, you will get an error because 'cowsay' is missing. It was only installed in the virtual environment:

Example

C:\Users\Your Name> python test.py

Result

Traceback (most recent call last):
  File "C:\Users\Your Name\test.py", line 1, in <module>
    import cowsay
ModuleNotFoundError: No module named 'cowsay'

Note: The virtual environment myfirstproject still exists, it is just not activated. If you activate the virtual environment again, you can execute the test.py file, and the diagram will be displayed.

Delete Virtual Environment

Another nice thing about working with a virtual environment is that when you, for some reason want to delete it, there are no other projects depend on it, and only the modules and files in the specified virtual environment are deleted.

To delete a virtual environment, you can simply delete its folder with all its content. Either directly in the file system, or use the command line interface like this:

Example

C:\Users\Your Name> rmdir /s /q myfirstproject