Best afterValues and names

Aliasing: two names, one list

Assigning one list to another name does not make a copy — both names point at the same list object. Change it through one name and the 'other' changes too. The matching reference ids in the state pane make the shared identity literal. Watch the backup get corrupted.

Make a backup of the scores list, then add 30 to the original — the backup should keep the first two scores.

Assignment doesn't copy a list execution-derived · CPython

variables

state after line 1 runs

variable	value
`scores`	`[10,20]`

step 1 / 3

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What you are looking at

Watch backup when only scores is touched — and watch the ref ids.

Buggy — backup = scores binds a second name to the same list (equal ref ids prove it). Appending 30 to scores changes backup too — it was never a separate copy.
Procedural — backup = scores[:] slices out a brand-new list, so the two are independent (no shared ref id). Now appending to scores leaves backup at [10, 20].

Every state you see came from running the program under CPython's tracer at build time — see how GlassBox stays honest.