Pop Element from List Property

This property describes how LW Python pops an element from a list, It first looks in the "Value" stack to get the index of the list in "Object Store. Then it pops the element at a given index (also specified in the "Value" stack) and updates the "Object Store" with the new list. More formally,

if the following are true:

  • expression state at time t = "call_function_begin"
  • Value Stack at time t = [ [ a, [ ] ], stack ]
  • the expression at time t = name."pop"(args)
  • value at obj in map (Variables Map at time t) = Python reference idx
  • the element at index idx of stack (Python Object Store at time t) = Python list entries

then Python Object Store at time (t + 1) = result of storing (Python list (stack after popping a value from stack entries at index a)) at index idx of stack (Python Object Store at time t)

For example,

if the following are true:

  • expression state at time 26 = "call_function_begin"
  • Value Stack at time 26 = [ [ 2, [ ] ], [ ] ]
  • the expression at time 26 = numbers.pop(2)
  • Python Object Store at time 26 = [ [2, 4, 6, 8, 10], [ ] ]

then Python Object Store at time (29 + 1) = result of storing (Python list (stack after popping a value from stack [ 2, [ 4, [ 6, [ 8, [ 10, [ ] ] ] ] ] ] at index 2)) at index 0 of stack (Python Object Store at time 29)

Here, LW Python read the list in index 0 of the "Object Store," popped the element at index 2 of this list, and then updated the "Object Store" with this new list.

Try stepping through the simulator to see LW Python pop 6 from "numbers."

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LW Python State
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LW Python Simulator

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