devsetup1-5  Exercise 3: pipx, and Choosing the Right Tool
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PART 1: pipx
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    pipx ensurepath          # once; log out and back in afterwards
    pipx install httpie
    pipx list
    command -v http
    http --version

Expected:
  - pipx list shows httpie and its version, and the commands it provides
    (http, https, httpie).
  - command -v http prints a path in ~/.local/bin (for example
    /home/you/.local/bin/http).
  - The tool works from any directory.

Show that its libraries are isolated:

    python3 -c "import httpie"

This fails with ModuleNotFoundError, because httpie's libraries live in its
own private environment, not in the system Python. (Look at
~/.local/share/pipx/venvs/httpie to see that environment.)

Clean up:
    pipx uninstall httpie

Note where the command lives: ~/.local/bin is the "installed for one user,
outside apt" location from Chapter 3. dpkg -S ~/.local/bin/http would report
that no package owns it.

PART 2: CHOOSING THE TOOL
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1. A Flask project that needs Flask, SQLAlchemy and a few other libraries.
   -> A virtual environment inside the project (python3 -m venv .venv), with
      the packages recorded in requirements.txt. Libraries belong to a
      project, and the project should be reproducible.

2. A code formatter you want to run on any file from anywhere.
   -> pipx. It is a program, not a library for one project; pipx gives it a
      private environment and a normal command.

3. A project that must run on Python 3.11.
   -> pyenv, to build 3.11 (Debian 13 ships 3.13), then pyenv local 3.11.x
      in the project, and a venv created with that Python. The .python-version
      file records the choice.

4. A library needed by a program you installed with apt.
   -> apt, using the python3-NAME package. The program runs on the system
      Python, so its libraries should come from Debian and stay consistent
      with it. Do not pip install it.

5. A quick throwaway experiment with a package you have never used.
   -> A temporary virtual environment (for example in /tmp or a scratch
      folder). Create it, try the package, delete the folder. Nothing is left
      behind, and the system Python is untouched.

THE PATTERN
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Ask what you are installing:
  a library for a project        -> venv
  a command-line tool            -> pipx
  a different Python version     -> pyenv
  something the OS itself uses   -> apt

WHY THIS WORKS AS AN ANSWER
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Part 1 demonstrates isolation directly instead of just describing it. Part 2
reduces four tools to one question, so the choice becomes routine rather than
something to look up each time.