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Virtual Env

A virtual environment is an isolated Python system. 
 
python -m pip install --upgrade pip
pip install virtualenv

virtualenv ./my_env     # create

. my_env/bin/activate   # load and activate
pip list                # test env     
deactivate              # exit env

source my_env/bin/activate # second method
pip list
deactivate

: '
Package    Version
---------- -------
pip        22.3.1
setuptools 65.6.3
wheel      0.38.4
'
        
echo 'my_env/' > .gitignore

Venv

Use the venv module which is included in the standard library. 
 
python3 -m venv myenv

myenv\Scripts\activate # windows

source myenv/bin/activate # linux

Requirements

Save the list for requirements in order to used later (or on another computer). 
 
(.venv) pip freeze > requirements.txt
(.venv) pip install -r requirements.txt

Python Upgrade (Windows)

1. Download Python

Go to the official Python website: https://www.python.org/downloads/windows/ Download the “Windows x86-64 executable installer” (64-bit is standard for servers). You just need to use the right installer and options. The installer contains everything Python needs. Download exactly this file: 
 
Windows x86-64 executable installer
python-3.12-amd64.exe

2. Install

Run the installer -> Run as Administrator Add Python to PATH. Unblock the File: Windows marks files copied from another machine as 'from the internet' even if transferred by USB. Solution: - Right‑click python-3.13.0-amd64.exe - Properties - Check Unblock - Click OK - Run installer again Python on Windows is designed to support multiple versions installed at the same time. In Path, move the new version above the old one. 
 
python --version

3. Virtual Environments

Each project uses its own Python version. 
 
C:\Python312\python.exe -m venv venv312
venv312\Scripts\activate
Upgrade pattern (production-safe): - Install new Python side‑by‑side (PATH) - Create new venv with it - Reinstall dependencies - Switch service / app to new venv - Remove old venv when stable

3.1 Create a new virtual environment

From the application root directory: 
 
"D:\Program Files\Python312\python.exe" -m venv venv312

venv312\Scripts\python.exe --version
# Python 3.12.0

3.2 Reinstall dependencies 

 
cd D:\python-apps\pof_statistics\
.\venv312\Scripts\activate

(venv312) 
python.exe -m pip install --upgrade pip
pip install -r requirements.txt






Questions and answers:
Clink on Option to Answer




1. What is a virtual environment in Python?

  • a) An isolated Python environment with its own packages
  • b) A backup copy of the operating system

2. Why are virtual environments useful?

  • a) They isolate project dependencies from the system Python
  • b) They make Python programs run faster

3. What is the main difference between virtualenv and venv?

  • a) venv is included in the Python standard library
  • b) virtualenv only works on Windows

4. What happens when you activate a virtual environment?

  • a) Python uses the environment’s local packages and interpreter
  • b) Python deletes system-wide packages

5. Why should a virtual environment folder be added to .gitignore?

  • a) Because it can be recreated and should not be version-controlled
  • b) Because Git cannot track folders

6. What is the purpose of deactivating a virtual environment?

  • a) To return to the system’s global Python environment
  • b) To uninstall Python

7. Which tool is recommended when you want only standard-library tools?

  • a) venv
  • b) virtualenv


References: