Regarding python lists

Question

We see a lot of operations on lists using its index like L[index] and we get the value associated with that index in a particular list.

I have a doubt on what exactly is python doing when we say "get me an element at this particular index(L[index])".

Is L[index] like a pointer which points to a particular value in the list and is it the reason why the value is changed through the assignment L[index]=value in the same address unlike other variables?

Any help on this would be appreciated.

score 0 · Answer 1 · answered Aug 10 '17 at 18:48

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Is L[index] like a pointer which points to a particular value in the list ...

No. It is an indicator to the compiler that the __getitem__(), __setitem__(), or __delitem__() method (or their C-level equivalents) of the object should be called depending on which operation is required.

answered Aug 10 '17 at 18:48

Ignacio Vazquez-Abrams

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These methods can be called directly. One would call the ability to use `[ ]` syntactic sugar. – 2rs2ts Aug 10 '17 at 18:57
Sure, but it's syntactic sugar in C/etc. as well, equivalent to `(L + index)`. – Ignacio Vazquez-Abrams Aug 10 '17 at 18:59
Then how come is L[index] O(1) complexity? – Bhanu sri Aug 10 '17 at 18:59
@Bhanusri: `del L[index]` is **not** O(1). – Ignacio Vazquez-Abrams Aug 10 '17 at 19:00
is getting a value at a particular index (value=L[index]) O(1)? – Bhanu sri Aug 10 '17 at 19:05
For lists, yes. – Ignacio Vazquez-Abrams Aug 10 '17 at 19:06
can you please explain how? – Bhanu sri Aug 10 '17 at 19:12
Have you looked at the implementation yet? – Ignacio Vazquez-Abrams Aug 10 '17 at 19:15
implementation of the list? – Bhanu sri Aug 10 '17 at 19:16
@IgnacioVazquez-Abrams I was just adding some extra info for OP, not correcting you :) – 2rs2ts Aug 10 '17 at 19:41
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@2rs2ts: I understand, I was just adding a little bit to the conversation as well. – Ignacio Vazquez-Abrams Aug 10 '17 at 19:43
@Bhanusri Recommend [how is python list implemented](https://stackoverflow.com/questions/3917574/how-is-pythons-list-implemented) for more information – lincr Aug 11 '17 at 15:02

Regarding python lists

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