Challenge 3: Write a requirements.txt — Possible Solution
====================================================================

requests==2.31.0
flask==3.0.0
pytest==7.4.3

WHY THIS WORKS AS AN ANSWER
------------------------------
Each line follows the package==version format the chapter describes —
one package per line, with an exact version pinned using the ==
operator, matching the pattern shown for installing "requests" earlier
in the chapter.

Pinning an exact version (rather than leaving it unpinned) is what
makes a requirements.txt reproducible: running pip install -r
requirements.txt on a different machine, or months later, installs
the SAME versions every time, rather than whatever happens to be
newest at install time — which could introduce breaking changes the
original project was never tested against.

This file would be placed alongside the project's code (not inside a
venv folder, which per the chapter should typically stay
project-local and out of shared/version-controlled files), so that
anyone setting up the project — including a future venv on a
different machine — can recreate the exact same dependency set with a
single command.