Swap Cups (Python / tkinter)

Platforms tested: macOS. tkinter is cross-platform, so Linux, FreeBSD, and Windows (incl. ARM64) are expected to work and are planned for testing — not yet verified.

The "Three Cups" shell game, built up in stages with Python's standard-library tkinter GUI toolkit. A blue ball is hidden under one of three cups; a sequence of swaps (A = Left/Middle, B = Middle/Right, C = Left/Right) shuffles them, and you work out where the ball ended up.

Files (in order of growth)

File	What it adds
three_cups.py	The pure logic — hide the ball, apply swaps, find the ball (no GUI).
three_cups_gui.py	A first tkinter window using text-box "cups".
three_cups_canvas.py	Real cup shapes drawn on a Canvas; redraw-from-state each frame.
three_cups_animated.py	Swaps play out over time with root.after() (no freezing).
three_cups_interactive.py	Full game: ball hidden during play, green/blue "Roswell" dots blink over each swapping pair, and after the run you click a cup to lift it — the ball flashes 7× if found, otherwise the cup is empty.

Run

python3 three_cups_interactive.py

Requires Python 3 with tkinter (included in standard CPython on macOS/Windows; on some Linux distros install python3-tk).

Verifying on a new OS

tkinter ships with CPython but the Tk runtime is sometimes a separate package. Only that install step differs; the run command is the same everywhere:

OS	Install Tk	Run
Linux (Debian/Ubuntu)	sudo apt install python3 python3-tk	python3 three_cups_interactive.py
Linux (Fedora)	sudo dnf install python3 python3-tkinter	python3 three_cups_interactive.py
Linux (Arch)	sudo pacman -S python tk	python3 three_cups_interactive.py
FreeBSD	pkg install python3 py3XX-tkinter	python3 three_cups_interactive.py
Windows (incl. ARM64)	install Python from python.org (Tk is bundled)	py three_cups_interactive.py

(On FreeBSD the py3XX-tkinter name tracks your Python version, e.g. py311-tkinter.)

Functional check (same on every OS):

1. Pick a cup — it lifts and the ball flashes 7×.
2. Enter swaps (e.g. ABCAB) and press Play — green/blue dots blink over each pair.
3. When done, click a cup — the ball flashes 7× if found, else "Nothing under that cup."

When a platform passes, flip its badge from planned-lightgrey to tested-2ea44f (and add the matching topic).

Sibling ports

The same game also exists in SwiftUI and C++/wxWidgets.