""" Copying """ a = [[1, 2], ["str", "str"]] b = a b[0].append(3) # print(a) # print(b) print(b[0] is a[0])

In this code, a list a is assigned to the variable b, meaning both variables refer to the same object in memory.

When we do b[0].append(3), we modify the first nested list inside a and b simultaneously, since they point to the same object.

The output will be:

[[1, 2, 3], ['str', 'str']]
[[1, 2, 3], ['str', 'str']]
True

b[0] is a[0] returns True because they are the same object.

If you want to create a copy of the list so that changes in b do not affect a, you should use copying, for example, copy.deepcopy for nested structures.