Python 3

However I look at this, the 'position 0' case seems special as you return a different 'head'. The simplest option I could see was to treat it as a separate case.

I quite like the proposed naming and structure here of 'next_index' being the count, starting from 1, and running through the llist until you find the right point to do the insert... although maybe 'node_count' or something would be more technically correct than 'index'

def insertNodeAtPosition(llist, data, position):
    
    new_node = SinglyLinkedListNode(data)
    
    if position == 0:
        new_node.next = llist
        return new_head
    
    this = llist
    next_index = 1
    while next_index != position:
        this = this.next
        next_index += 1
    
    new_node.next = this.next
    this.next = new_node
    return llist