Setting variable to a list with lists inside as reference

Question

I'm trying to set area to List except if a wanted to change area, List would stay the same. So I did a for loop that would get each element from List and append it to area but that seems to almost be working, like if I was missing a step. Can somebody explain to me why it is not working? Preferably don't send code because I want to code it myself followed with an explanation, but if you really need to its fine.

List = [[1, 1, 1, 2, 1, 1, 1], [1, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 1], [2, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 1], [1, 1, 1, 1, 1, 1, 1]]
area = []
for Map_list in range(len(List)):
 area.append([])
 for Map_index in List[Map_list]:
 area[Map_list].append(List[Map_list][Map_index])

For comparison:

print(f'area: {area}')
print(f'List: {List}')

• revliscano: Could you share what's the output you want to get like?
• aaa: I want this output print(f'area: {area}') to be the same as this output print(f'List: {List}') But instead, the outputs are different
• revliscano: Isn't just area = [*List] what you want? By the way, it's nice to follow PEP8 styling when coding in Python. Try to use Snake Case when declaring variables. (list_ instead of List, map_list instead of Map_List and so on)
• aaa: That doesn't seem to be working, but thank you for the tip on using list_ instead
• revliscano: Yes, I'm sorry. I did not take in consideration that the elements of the list List were mutable objects (other lists). You are right, by doing just that, it would not word for that case.

Answer 1

The for Map_list loop sets Map_list successively to the index of each list in List so those sublists can be used as sources for copying.

The for Map_index in List[Map_list]: goes through the values, not the indexes of the elements of the sublist. But the statement

area[Map_list].append(List[Map_list][Map_index])

uses Map_index as an index, so it doesn't have the desired effect. It uses data from the sublist as an index on the sublist.

To get the desired effect of changes to area having no effect on List, you should use the deepcopy function from the copy module of the standard library. This also means you don't need your nested for-loops any more.

The suggested solution of area = [*List] solves the problem of making a list that looks the same, but does not satisfy the requirement that changes to List should not affect area. Demonstration:

>>> list1 = [[1]]
>>> list2 = [*list1]
>>> list1
[[1]]
>>> list2
[[1]]
>>> list1[0][0] = 99
>>> list1
[[99]]
>>> list2
[[99]]