为什么在LeetCode第23题中，变量A在不同上下文中有不同的含义？

<code># Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:
        if not lists:
            return None
        return self.mergeKList(lists, 0, len(lists) - 1)
<pre class="brush:php;toolbar:false;"><code>def mergeKList(self, lists: List[Optional[ListNode]], start: int, end: int) -> Optional[ListNode]:
    if start == end:
        return lists[start]

    mid = (start + end) // 2 
    left = self.mergeKList(lists, start, mid)
    right = self.mergeKList(lists, mid + 1, end) 
    return self.merge(left, right)

def merge(self, A, B):
    lead = ListNode()
    head = lead
    while A and B:
        if A.val < B.val:
            head.next = A
            A = A.next
        else:
            head.next = B
            B = B.next
        head = head.next
    if A:
        head.next = A
    else:
        head.next = B
    return lead.next</code></pre><p>在<code>merge</code>函数中的<code>while A and B</code>循环部分，变量A被理解为指向链表某个节点的引用：</p><pre><code class="python">while A and B:
if A.val < B.val:
    head.next = A
    A = A.next
else:
    head.next = B
    B = B.next
head = head.next</code></pre><p>在这段代码中，A确实是一个节点的引用，指向链表中的一个具体节点。然而，在<code>if A:</code>部分，A的含义有所不同：</p><pre><code class="python">if A:
head.next = A</code>