You can control the behavior manually, like: first = [0,1,2] second = [*a,3] # first is unchanged, second = [0,1,2,3] Or second=itertools.chain(first, [3]

You can control the behavior manually, like: first = [0,1,2] second = [*a,3] # first is unchanged, second = [0,1,2,3] Or second=itertools.chain(first, [3]), which avoids the copy. Though, to me, it's asking for trouble later.