Set Attribute Property

LW Python sets an attribute to a value by looking up the object in the "Object Store," adding or updating the object's attribute to the value, then replacing the existing object in the "Object Store" with the new object.

if the following are true:

Expression Stack at time t = [ [ ], [ [ obj.attribute = val, ys ], rest ] ]
Value Stack at time t = [ [ value, [ Python reference idx, [ ] ] ], [ next_level, other_levels ] ]
the element at index idx of stack (Python Object Store at time t) = Python object: entries

then Python Object Store at time (t + 1) = result of storing (Python object: (result of storing value at key: attribute in map: entries)) at index idx of stack (Python Object Store at time t)

For example, suppose that the following are true:

Expression Stack at time 23 = [ [ ], [ [ self."first_name" = first_name, [ ] ], [ ] ] ]
Value Stack at time 23 = [ [ "John", [ Python reference 0, [ ] ] ], [ [ ], [ ] ] ]
Python Object Store at time 23 = [ Python object: [ entry "__class_name__": "Person", [ ] ], [ ] ]

Here is a table view of the Object Store at time 23:

Index Type Contents

0 class instance __class_name__ Person

Index	Type	Contents
0	class instance	__class_name__	Person

We claim that

the element at index 0 of stack (Python Object Store at time 23) = Python object: [ entry "__class_name__": "Person", [ ] ]

Then we conclude that:

Python Object Store at time (23 + 1) = result of storing (Python object: (result of storing "John" at key: "first_name" in map: [ entry "__class_name__": "Person", [ ] ])) at index 0 of stack (Python Object Store at time 23)

We claim that

result of storing "John" at key: "first_name" in map: [ entry "__class_name__": "Person", [ ] ] = [ entry "__class_name__": "Person", [ entry "first_name": "John", [ ] ] ]

We also claim that

result of storing (Python object: [ entry "__class_name__": "Person", [ entry "first_name": "John", [ ] ] ]) at index 0 of stack [ Python object: [ entry "__class_name__": "Person", [ ] ], [ ] ] = [ Python object: [ entry "__class_name__": "Person", [ entry "first_name": "John", [ ] ] ], [ ] ]

Thus, we conclude that:

Python Object Store at time (23 + 1) = [ Python object: [ entry "__class_name__": "Person", [ entry "first_name": "John", [ ] ] ], [ ] ]

This simplifies to:

Python Object Store at time 24 = [ Python object: [ entry "__class_name__": "Person", [ entry "first_name": "John", [ ] ] ], [ ] ]

See here for the full proof.

Notice that the "Person" object initially does not have any attributes. But LW Python adds the following entry:

first_name:"John"

And then updates the Object Store with the new object.

Here is a table view of the Object Store at time 33:

Index Type Contents

0 class instance __class_name__ Person

first_name John

Index	Type	Contents
0	class instance	__class_name__	Person
first_name	John

Try stepping through the simulator to see LW Python update the "Person" object in the Object Store.

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