Python Virtual Environment
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
Run this command to create a virtual environment named myfirstproject:
C:\Users\Your Name> python -m venv myfirstproject
$ python -m venv myfirstproject
This will set up a virtual environment, and create a folder named "myfirstproject" with subfolders and files, like this:
Result
The file/folder structure will look like this:
myfirstproject
Include
Lib
Scripts
.gitignore
pyvenv.cfg
Activate Virtual Environment
To use the virtual environment, you have to activate it with this command:
Example
Activate the virtual environment:
C:\Users\Your Name> myfirstproject\Scripts\activate
$ source myfirstproject/bin/activate
After activation, your prompt will change to show that you are now working in the active environment:
Result
The command line will look like this when the virtual environment is active:
(myfirstproject) C:\Users\Your Name>
(myfirstproject) ... $
Install Packages
Once your virtual environment is activated, you can install packages in it, using
pip:
Example
Install Matplotlib in the virtual environment:
(myfirstproject) C:\Users\Your Name> pip install matplotlib
(myfirstproject) ... $ pip install matplotlib
Result
MatplotLib is installed only in the virtual environment:
Collecting matplotlib
Using cached matplotlib-3.10.1-cp313-cp313-win_amd64.whl.metadata (11 kB)
Collecting contourpy>=1.0.1 (from matplotlib)
Downloading contourpy-1.3.2-cp313-cp313-win_amd64.whl.metadata (5.5 kB)
Collecting cycler>=0.10 (from matplotlib)
Using cached cycler-0.12.1-py3-none-any.whl.metadata (3.8 kB)
Collecting fonttools>=4.22.0 (from matplotlib)
Downloading fonttools-4.57.0-cp313-cp313-win_amd64.whl.metadata (104 kB)
Collecting kiwisolver>=1.3.1 (from matplotlib)
Using cached kiwisolver-1.4.8-cp313-cp313-win_amd64.whl.metadata (6.3 kB)
Requirement already satisfied: numpy>=1.23 in c:\users\stale\myfirstproject\lib\site-packages (from matplotlib) (2.2.5)
Collecting packaging>=20.0 (from matplotlib)
Downloading packaging-25.0-py3-none-any.whl.metadata (3.3 kB)
Collecting pillow>=8 (from matplotlib)
Downloading pillow-11.2.1-cp313-cp313-win_amd64.whl.metadata (9.1 kB)
Collecting pyparsing>=2.3.1 (from matplotlib)
Using cached pyparsing-3.2.3-py3-none-any.whl.metadata (5.0 kB)
Collecting python-dateutil>=2.7 (from matplotlib)
Using cached python_dateutil-2.9.0.post0-py2.py3-none-any.whl.metadata (8.4 kB)
Collecting six>=1.5 (from python-dateutil>=2.7->matplotlib)
Using cached six-1.17.0-py2.py3-none-any.whl.metadata (1.7 kB)
Using cached matplotlib-3.10.1-cp313-cp313-win_amd64.whl (8.1 MB)
Downloading contourpy-1.3.2-cp313-cp313-win_amd64.whl (223 kB)
Using cached cycler-0.12.1-py3-none-any.whl (8.3 kB)
Downloading fonttools-4.57.0-cp313-cp313-win_amd64.whl (2.2 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 2.2/2.2 MB 46.0 MB/s eta 0:00:00
Using cached kiwisolver-1.4.8-cp313-cp313-win_amd64.whl (71 kB)
Downloading packaging-25.0-py3-none-any.whl (66 kB)
Downloading pillow-11.2.1-cp313-cp313-win_amd64.whl (2.7 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 2.7/2.7 MB 92.3 MB/s eta 0:00:00
Using cached pyparsing-3.2.3-py3-none-any.whl (111 kB)
Using cached python_dateutil-2.9.0.post0-py2.py3-none-any.whl (229 kB)
Using cached six-1.17.0-py2.py3-none-any.whl (11 kB)
Installing collected packages: six, pyparsing, pillow, packaging, kiwisolver, fonttools, cycler, contourpy, python-dateutil, matplotlib
Successfully installed contourpy-1.3.2 cycler-0.12.1 fonttools-4.57.0 kiwisolver-1.4.8 matplotlib-3.10.1 packaging-25.0 pillow-11.2.1 pyparsing-3.2.3 python-dateutil-2.9.0.post0 six-1.17.0
[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 Matplotlib module is installed in your virtual environment, lets use it to display a diagram.
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
Insert three lines in test.py:
import matplotlib.pyplot as plt
plt.plot([0, 6], [0, 250])
plt.show()
Then, try to execute the file while you are in the virtual environment:
Example
Execute test.py in the virtual environment:
(myfirstproject) C:\Users\Your Name> python test.py
(myfirstproject) ... $ python test.py
As a result, you will get a diagram showing a line plot from position 0, 0 to 6, 250:
Result
Deactivate Virtual Environment
To deactivate the virtual environment use this command:
Example
Deactivate the virtual environment:
(myfirstproject) C:\Users\Your Name> deactivate
(myfirstproject) ... $ deactivate
As a result, you are now back in the normal command line interface:
Result
Normal command line interface:
C:\Users\Your Name>
$
If you try to execute the test.py file outside of the virtual environment, you will get an error because Matplotlib is missing. It was only installed in the virtual environment:
Example
Execute test.py outside of the virtual environment:
C:\Users\Your Name> python test.py
$ python test.py
Result
Error because Matploblib is missing:
Traceback (most recent call last):
File "C:\Users\Your Name\test.py", line 1, in <module>
import matplotlib.pyplot as plt
ModuleNotFoundError: No module named 'matplotlib'
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
Delete myfirstproject from the command line interface:
C:\Users\Your Name> rmdir /s /q myfirstproject
$ rm -rf myfirstproject
