Linked List Block Reversal

1def reverseKGroup(head: Optional[ListNode], k: int) -> Optional[ListNode]:
2    dummy = ListNode(0)
3    dummy.next = head
4    group_prev = dummy
5    while True:
6        kth = group_prev
7        for _ in range(k):
8            kth = kth.next
9            if not kth:
10                return dummy.next
11        group_next = kth.next
12        prev, cur = group_next, group_prev.next
13        while cur != group_next:
14            nxt = cur.next
15            cur.next = prev
16            prev = cur
17            cur = nxt
18        tmp = group_prev.next
19        group_prev.next = kth
20        group_prev = tmp