is this a infinite dimensional list

Question

Does this code create an infinitely deep list?

foo = ['Hello']
bar = [foo]*100
foo[0] = bar
print foo
print foo[0] == foo
print foo == bar

Because that is what it seems like, but how is it not taking up infinite amounts of memory then, everything is still running smoothly. Does it take up less memory because of pointers? Also, if I were to get to the bottom what value would I find? Where has the original 'Hello' gone in the computer's memory?

Note:
this is not a duplicate, because of the last question.

Can you please place your code in the question also? – Glorious Kale Dec 15 '14 at 00:14 — Glorious Kale, Dec 15 '14 at 00:14

score 4 · Accepted Answer · answered Dec 15 '14 at 00:13

4

No, it creates two lists: one with a single item, and one with 100 items that all point to the first list. It then makes the single item in the first list point to the second list.

So it does not make an infinitely deep list; it just creates a cycle. If you created a loop that tried to continuously read the first element of the current item and then recurse, it would run infinitely (or at least, it would run until it hit Python's recursion limit), but that's because it's just going in circles.

Just like a circle doesn't have an infinite circumference - it has a finite circumference, but that doesn't mean you can't keep going around in circles forever.

answered Dec 15 '14 at 00:13

Amber

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I like the circle analogy I think it helps clarify what's happening. – Matt Coubrough Dec 15 '14 at 00:16
So it is not a infinite dimensional list it only acts like one? And also assume it is possible, what would I find at the bottom? the original value? – tox123 Dec 15 '14 at 00:18
1

What "bottom"? That's like asking what you would find when you got to the corner of a circle. :) – Amber Dec 15 '14 at 00:21
@Amber but aren't you always at the corner of a circle? – tox123 Jul 11 '15 at 22:06

is this a infinite dimensional list

1 Answers1