pll_2.py

class SinglyLinkedList:
    """A singly linked list implementation"""

    def __init__(self) -> None:
        """Initialize a singly link list where the head is None"""
        self.head = None

    def __str__(self) -> str:
        """Return a string representation of the linked list"""
        sll_nodes = []
        current_node = self.head
        while current_node is not None:
            sll_nodes.append(str(current_node.data))
            current_node = current_node.next_node
        sll_nodes.append(str(None))
        return " -> ".join(sll_nodes)