Merge Two Sorted Lists

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        # Handle edge cases where either or both lists are None
        if not l1:
            return l2
        if not l2:
            return l1

        result_head = None
        result_tail = None

        # Keep track of pointers #1 and #2
        p1 = l1
        p2 = l2

        # While neither pointer #1 and #2 have reached end of their respective LLs:
        while p1 and p2:

            # If p1 <= p2:
            if p1.val <= p2.val:

                # Keep track of p1's original next node
                l1_next_node = p1.next
                # Reset p1.next to avoid circular pointers
                p1.next = None

                # Add p1 to result
                # If this is the 1st node in the result, set result head
                if not result_head:
                    result_head = p1
                # If this is NOT the 1st node in the result, add p1 to end of result
                else:
                    result_tail.next = p1
                # Increment result_tail
                result_tail = p1

                # Increment p1
                p1 = l1_next_node

            # Else (if p2 > p1)
            else:
                # Add p2 to result
                l2_next_node = p2.next
                p2.next = None

                if not result_head:
                    result_head = p2
                else:
                    result_tail.next = p2
                # Increment result_tail
                result_tail = p2

                # Increment p2
                p2 = l2_next_node

        # If p1 is None:
        if not p1:
            # Add rest of p2's list to result
            result_tail.next = p2
        # Else
        else:
            # Add rest of p1's list to result
            result_tail.next = p1

        # Return result_head
        return result_head