List Get Item Property

This property describes how Python retrieves an element from a list in the "Object Store."

For example, suppose that the following are true:

• expression state at time 23 = "call_function_begin"
• Value Stack at time 23 = [ [ 1, [ Python reference 0, [ ] ] ], [ ] ]
• the expression at time 23 = __getitem__(numbers, 1)
• Python Object Store at time 23 = [ [2, 4, 6], [ ] ]

First, we know that:

the element at index 0 of stack (Python Object Store at time 23) = [2, 4, 6]

Then we can conclude that:

Return Value at time (23 + 1) = the element at index 1 of stack [ 2, [ 4, [ 6, [ ] ] ] ]

We also know that:

the element at index 1 of stack [ 2, [ 4, [ 6, [ ] ] ] ] = 4

Thus, we can conclude that:

Return Value at time (23 + 1) = 4

Which simplifies to:

Return Value at time 24 = 4

The value stack tells LW Python that the "numbers" list is stored in index 0. And we can see that there is a list [2, 4, 6] in index 0 of the "Object Store." Then at time 24, the return value is the element at index 1 of the list [2, 4, 6], which is 4.

See the full proof here.

Try stepping through the simulator to see LW Python retrieve the element from the list in the "Object Store."

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