Create Virtual environment and install libraries for Python

Learn library management in python using Virtual environment, an alternate to Conda. Learn how it works, with example.

┌───(.venv)-[D:\Programming\TESTING]
└─[$] python
Python 3.13.12 
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Welcome to Python venv")
Welcome to Python venv

for Linux OS : substitute python by python3

Create Virtual environment

• check python version : python --version
• create a virtual environment named .venv : python -m venv .venv

In Linux, we create a hidden file/folder using . prefix. For example, .venv

• activate virtual env : .venv\Scripts\activate (Windows), .venv/bin/activate (Linux)
• deactivate : deactivate
• check python location : where.exe python (Windows), which python3 (Linux).

Example

See the workflow in PowerShell. (Same workflow for Linux)

Windows PowerShell
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Install the latest PowerShell for new features and improvements! https://aka.ms/PSWindows


┌───[D:\Programming\TESTING]
└─[$] python --version
Python 3.13.12

┌───[D:\Programming\TESTING]
└─[$] where.exe python
C:\Users\photon\AppData\Local\Microsoft\WindowsApps\python.exe   <--- Global Python location

┌───[D:\Programming\TESTING]
└─[$] python -m venv .venv

┌───[D:\Programming\TESTING]
└─[$] .venv\Scripts\activate

┌───(.venv)-[D:\Programming\TESTING]
└─[$] python --version
Python 3.13.12

┌───(.venv)-[D:\Programming\TESTING]
└─[$] where.exe python     <--- detect two python
D:\Programming\TESTING\.venv\Scripts\python.exe     <--- Python in Venv
C:\Users\photon\AppData\Local\Microsoft\WindowsApps\python.exe

┌───(.venv)-[D:\Programming\TESTING]
└─[$] python -m pip --version
pip 25.3 from D:\Programming\TESTING\.venv\Lib\site-packages\pip (python 3.13)

┌───(.venv)-[D:\Programming\TESTING]
└─[$] deactivate

┌───[D:\Programming\TESTING]
└─[$] where.exe python
C:\Users\photon\AppData\Local\Microsoft\WindowsApps\python.exe

┌───[D:\Programming\TESTING]
└─[$]

Install pip and packages

• check version : python -m pip --version
• install pip : python -m pip install --upgrade pip
• install single package NumPy via : python -m pip install numpy
• for multiple packages create requirements.txt : vim requirements.txt
• paste (p) inside requirements.txt :

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numpy
matplotlib
scipy
pandas
requests

• install packages inside requirements.txt : pip install -r requirements.txt
• uninstall all : pip uninstall -r requirements.txt -y
• details of package : pip show numpy
• list of packages installed : pip list
• identifying outdated packages: pip list --outdated

Example

See how venv affects the work flow. Lets install the NumPy library for our project.

┌───[D:\Programming\TESTING]
└─[$] .venv\Scripts\activate

┌───(.venv)-[D:\Programming\TESTING]
└─[$] python -m pip install numpy
Collecting numpy
  Using cached numpy-2.4.4-cp313-cp313-win_amd64.whl.metadata (6.6 kB)
Using cached numpy-2.4.4-cp313-cp313-win_amd64.whl (12.3 MB)
Installing collected packages: numpy

┌───(.venv)-[D:\Programming\TESTING]
└─[$] python
Python 3.13.12 
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> x = np.array([1,2,3])
>>> np.sum(x)
np.int64(6)
>>> quit

┌───(.venv)-[D:\Programming\TESTING]
└─[$]

What happens if you don’t activate venv ?

┌───[D:\Programming\TESTING]
└─[$] python
Python 3.13.12
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import numpy
ModuleNotFoundError: No module named 'numpy'
>>> quit

┌───[D:\Programming\TESTING]
└─[$]

It gives ModuleNotFoundError, since NumPy is not globally installed (inside c:\users\photon\appdata\local\packages\pythonsoftwarefoundation.python.3.13_qbz5n2kfra8p0\localcache\local-packages\python313\site-packages).

Update and Upgrade

• update pip : python -m pip install --upgrade pip
• upgrade all packages: pip install pip-upgrade-all then execute pip-upgrade-all

Notes

Its better to keep the project inside the parent directory where \.venv is installed (say, D:\Programming\TESTING\Project ). The file structure looks like the following.

D:\Programming\TESTING
│
├── .venv          <------ Do not alter this folder
|    ├── Include
|    ├── Lib
|    ├── Script
|    |    ├── activate
|    |    └── Activate.ps1
|    ├── share
|    ├── .gitignore
|    └── pyvenv.cfg
│
└── Project
     ├── BoltzmannMachine.py
     └── AutoEncoder.py

If you use VS Code (and ‘open folder’ D:\Programming\TESTING), it will automatically activate the virtual environment for the project as shown below, you do not have apply .venv\bin\activate.

----- VS Code Terminal ------

┌───[D:\Programming\Python] 
└─[$] & d:\Programming\Python\.venv\Scripts\Activate.ps1 <--- Run automatically
 
┌───(.venv)-[D:\Programming\Python] 
└─[$] █ you start from here

Reference

For detailed knowledge, refer to https://packaging.python.org/en/latest/guides/installing-using-pip-and-virtual-environments/.