By using collections.deque or self implementation example below:

#!/usr/bin/env python3

class LinkedList():
    def __init__(self, data=None):
        self.head = None

        if data is not None:
            node = Node(data.pop(0))
            self.head = node
            for d in data:
                node.next = Node(d)
                node = node.next

    def add_tail(self, node):
        if self.head is None:
            self.head = node
            return self

        ln = None
        for n in self:
            ln = n
        ln.next = node

        return self

    def add_head(self, node):
        if self.head is None:
            self.head = node
            return self

        if node.next is not None:
            ln = node.next
            while ln.next is not None:
                ln = ln.next
        else:
            ln = node

        ln.next = self.head
        self.head = node

    # def __next__(self) # NOTE dont need with yield, generator class does the __next__

    def __iter__(self):
        node = self.head

        while node is not None:
            yield node
            node = node.next

    def __str__(self):
        return str([n._d for n in self])


class Node():
    def __init__(self, data):
        self._d = data
        self.next = None

if __name__ == "__main__":
    ll = LinkedList([1, 2, 3])
    print(ll) # [1, 2, 3]
    n = Node(4)
    n.next = Node(5)
    ll.add_tail(n).add_tail(Node(6))
    print(ll) # [1, 2, 3, 4, 5, 6]
    n2 = Node(-1)
    n2.next = Node(0)
    ll.add_head(n2)
    ll.add_head(Node(-2))
    print(ll) # [-2, -1, 0, 1, 2, 3, 4, 5, 6]