🐍 How Python venv Works

venv (short for virtual environment) is Python’s built-in tool for creating isolated environments.
It lets you install dependencies on a per-project basis without affecting your system Python or other projects.

---

⚙️ What It Actually Is

A virtual environment is just a directory that contains:

.venv/
├── bin/                # Executables (Python, pip, etc.)
│   ├── activate        # Shell script that sets environment vars
│   └── python          # Copy/symlink of the Python interpreter
├── lib/                # Site-packages live here
│   └── python3.x/
│       └── site-packages/
└── pyvenv.cfg          # Metadata (points to base Python install)

There is no background process or runtime service.
It’s purely a self-contained folder structure.

---

🧩 Lifecycle

Step	Command	Description
Create	python3 -m venv .venv	Creates a new environment folder with a copy of Python.
Activate	source .venv/bin/activate	Temporarily adds .venv/bin to your PATH and sets VIRTUAL_ENV.
Deactivate	deactivate	Restores your shell to normal.
Delete	rm -rf .venv	Completely removes the environment and its packages.

Activation only modifies the current shell session.
The environment itself persists until you delete it.

---

📦 Installing Packages

Once activated, installing packages with pip goes into the local environment:

source .venv/bin/activate
pip install requests

The package will be installed in .venv/lib/python3.x/site-packages/, and will not affect your system Python or global pip environment.

---

🔍 Quick Sanity Check

which python
# → /path/to/project/.venv/bin/python

python -m site
# Shows local site-packages path inside .venv

If both point inside .venv, you’re isolated correctly.

---

💡 Pro Tips

• Add .venv/ to your .gitignore — it’s per-user, not per-repo.

• If you use requirements.txt, recreate the venv anytime by running:

  python3 -m venv .venv
  source .venv/bin/activate
  pip install -r requirements.txt

• Each project can have its own interpreter and dependency versions.

---

✅ Summary: venv is not a process — it’s a directory-based isolation mechanism. It persists until you delete it and only changes your shell’s environment temporarily when activated.