List b’s value also changing for each iteration..why?

Question

https://code.sololearn.com/cA0A15a3A21a/?ref=app

Answer 1

Muhammed Niyas, maybe you should append a copy of l on line 36:

if z == "print":
b.append(l.copy())

Answer 2

but why I cant append l? John Robotane

Answer 3

Becouse in python variables are actually references to objects

l=[] means that 'l' referes to a new void list

b=[] means same thing

b.append(l) means that the object pointed by 'l' is now also pointed by the last element of b

Tha means that every time you modify that list object trough 'l' you will see it also trough b

This will happen until the "reverse" case because
l = l[::-1] does not modify the list object itself, but creates a new object and now 'l' referes to it