For those reading this in the future: I wanted to debug linked list problems on a local environment so here is what I did.

1. Modified the Leetcode code for ListNode by including the dunder "repr" method. This is for when you want to print a ListNode to see what its value and next node(s).

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

    def __repr__(self):
        return "ListNode(val=" + str(self.val) + ", next={" + str(self.next) + "})"

2. Next, I made a recursive function that makes a nested ListNode when you pass in a list. This is so you can test your methods by passing in lists (instead of having to manually make a confusing looking ListNode yourself.

def list_to_LL(arr):
    if len(arr) < 1:
        return None

    if len(arr) == 1:
        return ListNode(arr[0])
    return ListNode(arr[0], next=list_to_LL(arr[1:]))

3. Here is an example that tests my answer for the "reverseList" problem:

def reverseList(head: ListNode) -> ListNode:
    prev = None
    while head:
        next_node = head.next
        head.next = prev
        prev = head
        head = next_node

    return prev


# test cases
t1 = list_to_LL([1, 2, 3, 4, 5])  #ListNode(val=1, next={ListNode(val=2, next={ListNode(val=3, next={ListNode(val=4, next={ListNode(val=5, next={None})})})})})
t2 = list_to_LL([1, 2])  #ListNode(val=1, next={ListNode(val=2, next={None})})
t3 = list_to_LL([])

# answers
print(reverseList(t1))
print(reverseList(t2))
print(reverseList(t3))