virtualenv

virtualenv is a powerful tool used for creating isolated Python environments. In Python development, different projects often require different versions of libraries, or even different versions of Python itself. Without virtualenv (or similar tools like venv), installing project-specific dependencies globally could lead to conflicts and break other projects or even the system's Python installation.

virtualenv solves this by creating a self-contained directory that includes a Python interpreter, the pip package installer, and its own site-packages directory. When you activate a virtual environment, your system's PATH is modified so that the `python` and `pip` commands point to the versions within that specific environment. This ensures that any libraries you install or any scripts you run only affect that particular environment, leaving your global Python installation untouched and preventing dependency clashes between projects.

Key benefits of using virtualenv include:
- Isolation: Each project gets its own set of dependencies, avoiding conflicts.
- Reproducibility: You can easily recreate the exact environment for a project on a different machine using a `requirements.txt` file.
- Cleaner Development: Keeps your global Python installation clean and stable.
- Easier Deployment: Helps ensure that your application runs with the correct dependencies in production.

While Python 3.3+ includes `venv` as a built-in module which serves a similar purpose, virtualenv remains widely used, especially for compatibility with older Python versions or when advanced features not present in `venv` are required.

 1. Install virtualenv (if not already installed globally)
pip install virtualenv

 2. Create a new virtual environment named 'my_project_env'
 This creates a directory 'my_project_env' in your current location
virtualenv my_project_env

 3. Activate the virtual environment
 On Linux/macOS:
source my_project_env/bin/activate
 On Windows (Command Prompt):
my_project_env\Scripts\activate.bat
 On Windows (PowerShell):
my_project_env\Scripts\Activate.ps1

 You'll see the environment's name (e.g., '(my_project_env)') in your terminal prompt, indicating it's active.

 4. Install a package within the activated environment
pip install requests

 5. List installed packages in the environment
pip freeze

 6. Create a simple Python script to demonstrate isolation
echo "import requests; print(f'Requests version: {requests.__version__}')" > test_requests.py
python test_requests.py
 Expected output: Requests version: X.Y.Z (where X.Y.Z is the version installed in the virtual environment)

 7. Deactivate the virtual environment
deactivate

 8. Verify isolation (requests should not be found globally unless already installed globally)
 After deactivating, try running the script again without requests installed globally:
 python test_requests.py  This would likely raise a ModuleNotFoundError if requests is not globally installed.

 9. (Optional) Remove the virtual environment
 Simply delete the directory (ensure you have deactivated it first)
rm -rf my_project_env  On Linux/macOS
 On Windows (Command Prompt): rmdir /s /q my_project_env