teaching_basics

Teaching Basics — visual Python fundamentals

Small, self-contained scripts that make the invisible parts of a program visible: loop counters, branch decisions, and data-structure state — shown both on screen (turtle) and as a printed trace that matches what a debugger's variable panel shows.

Each file teaches exactly one idea. Run them one at a time.

The lessons (run in order)

File	Concept	What students watch
01_while_loop.py	while loop	A square spirals out while side < MAX. The loop variable, its step, and the condition are printed each pass. Comment out the side += step line to demonstrate an infinite loop.
02_if_conditions.py	if / elif / else	Visual FizzBuzz — each number becomes a colored dot showing which branch was taken. Teaches that order matters (15 before 3 and 5).
03_lists.py	lists	A list drawn as a bar chart that redraws after every append / pop / sort. The picture and the printed list always match.
04_stack_vs_queue.py	stack vs queue	Same items pushed into both; removal shows LIFO vs FIFO order side by side.
05_cube_3d.py	data structures + loops + 3D	A spinning cube built from a list of vertices and a list of edges. Connects to ../cam_toolpath_paraboloid.py.
06_debug_dataflow.py	debugging dataflow	Has a deliberate bug that crashes with ZeroDivisionError. Students trace the bad value back to its source instead of guessing — the crash is downstream of the real cause.
07_for_loop.py	for loop + range()	One dot per value in range(start, stop, step); shows the sequence range builds and that stop is excluded.
08_dictionary.py	dictionary	Key→value pairs drawn as labeled boxes; redraws on add, update (same key replaces, not duplicates), and lookup.

How to teach debugging with these (VS Code)

1. Print-tracing first. Every script prints a trace. Run it and read the trace line-by-line next to the code. This builds the mental model of "the program has state, and state changes one step at a time."

2. Then the debugger. Open 06_debug_dataflow.py:

   • Click in the gutter on the line marked # <-- breakpoint here to set a red dot.
   • Press F5 (Run and Debug → Python File).
   • When it pauses, look at the Variables panel — you'll see total is correct but count is 0. That mismatch is the bug.
   • Use Step Over (F10) to walk one line at a time and watch values change.

3. The big idea — dataflow. A bug usually shows up downstream of its cause (the crash is at the division, but the real problem is the missing count += 1). Debugging = follow the wrong value back to the last place it was right.

Suggested classroom flow

• Run a script, predict the output before it finishes, then check.
• Change ONE constant at the top (e.g. MAX_SIDE, TURNS) and predict the effect.
• Break it on purpose (remove the loop step, swap elif order) and watch it fail.
• Fix 06_debug_dataflow.py live using a breakpoint.

Running

python teaching_basics/01_while_loop.py

Turtle windows close on click. 06_debug_dataflow.py runs in the terminal only.