devsetup1-5  Exercise 2: A Virtual Environment Is Disposable
============================================================

COMMANDS
--------
    mkdir -p ~/projects/disposable && cd ~/projects/disposable

    # BEFORE activation
    type -a python3

    python3 -m venv .venv
    source .venv/bin/activate

    # DURING activation
    type -a python3
    pip --version

    pip install requests
    pip freeze > requirements.txt
    cat requirements.txt

    deactivate

    # AFTER deactivation
    type -a python3

    # Destroy the environment completely
    rm -rf .venv

    # Rebuild it from the list
    python3 -m venv .venv
    source .venv/bin/activate
    pip install -r requirements.txt
    python3 -c "import requests; print(requests.__version__)"
    deactivate

WHAT type -a python3 REPORTS
----------------------------
Before:  /usr/bin/python3 only.
During:  /home/you/projects/disposable/.venv/bin/python3 FIRST, then
         /usr/bin/python3. The shell runs the first one, which is the venv's.
         pip --version also reports a path inside .venv.
After:   back to /usr/bin/python3 only.

This is the point of activation: it puts the environment's bin directory at
the front of PATH, so "python3" and "pip" resolve to the venv's copies. It
changes nothing about the system Python.

WHAT requirements.txt LOOKS LIKE
--------------------------------
    certifi==...
    charset-normalizer==...
    idna==...
    requests==...
    urllib3==...

pip freeze lists requests and everything it depends on, each pinned to the
exact version installed. Your version numbers will differ.

THE .gitignore
--------------
Check for it:  cat .venv/.gitignore
Since Python 3.13, python3 -m venv creates a .gitignore inside the
environment containing a single "*", so Git ignores the whole folder. You
commit requirements.txt (the recipe), not .venv (the result).

WHY THIS WORKS AS AN ANSWER
---------------------------
Deleting and rebuilding the environment turns "a venv is disposable" from a
claim into something you have watched happen. It also shows why the
requirements file matters more than the environment itself.