Deleting the tail node of a singly linked list involves traversing the list to find the second-to-last node and updating its next reference to None. This operation requires traversing the list to find the tail and the node before it.

Consider a singly linked list with the following structure before deletion:

```
Head -> 1 -> 2 -> 3 -> 4 -> None
```

We want to delete the tail node (node with value 4). Follow these steps:

**Check if the List is Empty**: If the head is None, the list is already empty, and there is nothing to delete.**Check if the List has Only One Node**: If the head's next reference is None, set the head to None, making the list empty.**Traverse to the Second-to-Last Node**: Start at the head and follow the next references until you reach the node before the last node (node with value 3).**Update the Second-to-Last Node's Next Reference**: Set the next reference of the second-to-last node to None, removing the last node from the list.

After performing these steps, the linked list will have the following structure:

```
Head -> 1 -> 2 -> 3 -> None
```

```
class Node:
def __init__(self, data):
self.data = data
self.next = None
class SinglyLinkedList:
def __init__(self):
self.head = None
def append(self, data):
new_node = Node(data)
if self.head is None:
self.head = new_node
else:
current = self.head
while current.next:
current = current.next
current.next = new_node
def delete_tail(self):
if self.head is None:
print("The list is already empty.")
return
if self.head.next is None:
self.head = None
return
current = self.head
while current.next.next:
current = current.next
current.next = None
def traverse(self):
current = self.head
while current:
print(current.data, end=" -> ")
current = current.next
print("None")
# Example usage:
linked_list = SinglyLinkedList()
linked_list.append(1)
linked_list.append(2)
linked_list.append(3)
linked_list.append(4)
print("Linked list before deleting tail:")
linked_list.traverse() # Output: 1 -> 2 -> 3 -> 4 -> None
linked_list.delete_tail()
print("Linked list after deleting tail:")
linked_list.traverse() # Output: 1 -> 2 -> 3 -> None
```

This Python program defines a singly linked list with methods for appending nodes, deleting the tail node, and traversing the list. The delete_tail method checks if the list is empty or has only one node, traverses to the second-to-last node, and updates its next reference to remove the last node from the list.