Immutable List

class IList:
    def __init__(self):
        self.item = None
        self.next = None

    def __add__(self, item):
        new_item = IList()
        new_item.item = item
        new_item.next = self
        return new_item

    def __getitem__(self, index):
        if index == 0:
            return self.item
        else:
            return self.next[index - 1]


Nil = IList()

my_list = Nil + 1 + 5 + 7 + 15 + 10

print(my_list[2])