Is there a way to set index 1 in a list when index 0 hasnt been defined

Question

In Java ByteCode there is an opcode called "istore_1", which stores the top value of the stack into index 1 of the local variables, a list. I am trying to replicate this in python, but if you set index 1 of an empty list, its gonna set index 0 rather than index 1. My idea was to check if the first index of the list is empty, and if it is set it to like "emptyindex" or something, but after I did some research, I didnt find a way to check if an index is empty. My question is now how to store a value into index 1 of a list, even if index 0 hasnt been set, and set index 0 to "emptyindex" as a placeholder. Thanks a lot :D

local_variables = []
stack = [1]

user = input("Enter instruction")
if user == "istore_1":
  local_variables.insert(1, stack[0])
print(local_variables)

Answer 1

You can use a function to manipulate your list:

def expand(a_list, index, value, empty=None):
    l = len(a_list)
    if index >= l:
        a_list.extend([empty]*(index + 1 - l))
    a_list[index] = value


local_variables = []

expand(local_variables, 1, 'str')

print(local_variables)

Output:

[None, 'str']