insert_at_index(self, index: int, value: object) -> None: This method inserts a new value at the specified index position in the linked list. Index 0 refers to the beginning of the list (right after the front sentinel). If the provided index is invalid, the method raises a custom "SLLException". Code for the exception is provided in the skeleton file. If the linked list contains N nodes (the sentinel node is not included in this count), valid indices for this method are [0, N] inclusive. Example #1: LinkedList () 1st test cases [(0, "A"), (0, "B"), (1, "c"), (3, "D"), (-1, "E"), (5, "F")) for index, value in test cases: print ("Inserted", value, "at index", index, ": ", end-"") try: 1st.insert_at_index (index, value) print (1st) except Exception as e: print (type (e)) Output: Inserted A at index 0: SLL (A) Inserted B at index 0: SLL (B -> A) SLL (B-> C -> A) Inserted C at index 1: Inserted D at index 3: SLL (B -> C -> A -> D) Inserted E at index -1 SLLException'>

class SLNode:
    """
    Singly Linked List Node class
    DO NOT CHANGE THIS CLASS IN ANY WAY
    """
    def __init__(self, value: object, next=None) -> None:
        self.value = value
        self.next = next

from SLNode import *


class SLLException(Exception):
    """
    Custom exception class to be used by Singly Linked List
    DO NOT CHANGE THIS CLASS IN ANY WAY
    """
    pass


class LinkedList:
    def __init__(self, start_list=None) -> None:
        """
        Initialize new linked list
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        self._head = SLNode(None)

        # populate SLL with initial values (if provided)
        # before using this feature, implement insert_back() method
        if start_list is not None:
            for value in start_list:
                self.insert_back(value)

    def __str__(self) -> str:
        """
        Return content of singly linked list in human-readable form
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        out = 'SLL ['
        node = self._head.next
        while node:
            out += str(node.value)
            if node.next:
                out += ' -> '
            node = node.next
        out += ']'
        return out

    def length(self) -> int:
        """
        Return the length of the linked list
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        length = 0
        node = self._head.next
        while node:
            length += 1
            node = node.next
        return length

    def is_empty(self) -> bool:
        """
        Return True is list is empty, False otherwise
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        return not self._head.next

def insert_at_index(self, index: int, value: object) -> None:
    """
     this implementation
    """
    pass