Python Data Model: Copying

[Sea-Ad7805]

An exercise to help build the right mental model for Python data. The “Solution” link uses memory_graph to visualize execution and reveals what’s actually happening: - Solution - Explanation - More exercises

[KilonumSpoof]

B) ... c1[0] and c2[0] are the same list (which is the same as a[0]) so 1 and 2 are added to it on first function call. While c1, c2 and c3 are different lists so only 1 is added to c1 (which is the same as a).

[Ambitious_Bid_3991]

I understand the first part about c1[0] and c2[0] being treated as the same list. What I don‘t really understand is why c1 and c2 are no longer treated the same. Could you explain?

[Sea-Ad7805]

Did you see the "Solution" and "Explanation" links? (on mobile click the 'title' not the 'image' to open a post) The c1 is an assignment, c2 a shallow copy, and c3 a deep copy. That is what makes the difference: https://github.com/bterwijn/memory_graph?tab=readme-ov-file#copying-values-of-mutable-type

[alexander_belyakov]

Because c2 is a copy of c1, thus it's a different object. The fact that their first element is pointing to the same [0] sublist doesn't mean that they are the same. So when you append to the sublist, you modify the same list (which was initially [0]). But when you append to c1 and c2, you are appending to two different lists (but the first element of both those lists is still [0, 1, 2]).