如何清除此 AttributeError “nonetype”？

Question

我在编译这个 mergesort linkedlist 时正在学习数据结构。我得到了这个错误。我尝试了很多但没有奏效。谁能告诉我出了什么问题？请。

Traceback（最近一次调用最后一次）： 文件“C:\Users**\AppData\Local\Programs\Python\Python37\merge_sort_ver_2.0 链表.py”，第 122 行，在

     sorted_list=merge_sort(lst)

文件“C:\Users**\AppData\Local\Programs\Python\Python37\merge_sort_ver_2.0 链表.py”，第 75 行，在 merge_sort 中

return merge(left,right)

文件“C:\Users**\AppData\Local\Programs\Python\Python37\merge_sort_ver_2.0 链表.py”，第 94 行，合并中

left_head=left.head

AttributeError: 'NoneType' 对象没有属性 'head'

def merge_sort(ll):
    if ll.length()==1:
        return ll
    elif ll.head is None:
        return ll
    left_half,right_half=split(ll)
    left=merge_sort(left_half)
    right=merge_sort(right_half)
    return merge(left,right)
def split(ll):
    if ll.head==None or ll==None:
        left_half=ll
        right_half=None
        return left_half,right_half
    else:
        size=ll.length()
        mid=size//2
        mid_node=ll.nodeAt(mid-1)
        right_half=ll
        left_half=LinkedList()
        left_half.head=mid_node.next
        mid_node.next=None
        return left_half,right_half
def merge(left,right):
    merged=LinkedList()
    merged.tailinsert(0)
    current=merged.head
    left_head=left.head
    right_head=right.head
    
    while left_head or right_head:
        if left_head is None:
            current.next=right_head
            right_head=right_head.next
        elif right_head is None:
            current.next=left_head
            left_head=left_head.next
        else:
    merged.head=head
    return merged.printlist()
lst=LinkedList()
lst.tailinsert(14)
lst.tailinsert(46)
lst.tailinsert(43)
lst.tailinsert(27)
sorted_list=merge_sort(lst)
print(sorted_list)

Answer 1

感谢 Jérômei 的提示，我清除了错误

def merge_sort(ll):

    if ll.length()==1:
        return ll
    elif ll.head is None:
        return ll
        
    
    left_half,right_half=split(ll)
    left=merge_sort(left_half)
    right=merge_sort(right_half)
    return merge(left,right)

def split(ll):

    if ll.head==None or ll==None:
        left_half=ll
        right_half=None
        return left_half,right_half
    else:
        size=ll.length()
        mid=size//2
        mid_node=ll.nodeAt(mid-1)
        right_half=LinkedList()
        left_half=ll
        right_half.head=mid_node.next
        mid_node.next=None
        return left_half,right_half


def merge(left,right):
    merged=LinkedList()
    merged.tailinsert(0)
    current=merged.head
    left_head=left.head
    right_head=right.head
    while left_head and right_head :
        left_data=left_head.data
        right_data=right_head.data
        if left_data < right_data:
            current.next=left_head
            left_head=left_head.next
        elif right_data <left_data:
            current.next=right_head
            right_head=right_head.next
        current=current.next    
            
    while right_head is not  None  :
        current.next=right_head
        right_head=right_head.next
        current=current.next
    while left_head is not None  :
        current.next=left_head
        left_head=left_head.next    
        current=current.next
         
    current=current.next        
    head=merged.head.next
    merged.head=head
    print("merged 1:")        
    merged.printlist()      

    return merged
lst=LinkedList()
lst.tailinsert(14)
lst.tailinsert(46)
lst.tailinsert(43)
lst.tailinsert(27)
merge_sort(lst)

**output:
merged 1:
14
46
merged 1:
27
43
merged 1:
14
27
43
46**

Answer 2

def merge_sort(ll):
    if ll.length()==1:
        return ll
    elif ll.head is None:
        return ll                    # Here, you return None
    left_half,right_half=split(ll)
    left=merge_sort(left_half)       # Then by recursion, here left=None
    right=merge_sort(right_half)
    return merge(left,right)         # Then you inject it in merge

def split(ll):
    if ll.head==None or ll==None:
        left_half=ll
        right_half=None
        return left_half,right_half
    else:
        size=ll.length()
        mid=size//2
        mid_node=ll.nodeAt(mid-1)
        right_half=ll
        left_half=LinkedList()
        left_half.head=mid_node.next
        mid_node.next=None
        return left_half,right_half

def merge(left,right):                # Then here, left is None
    merged=LinkedList()
    merged.tailinsert(0)
    current=merged.head
    left_head=left.head               # Then boom because None.head
    right_head=right.head

现在，介绍一些方法。

遇到此类错误时，请使用print 显示函数的参数。这对你有很大帮助。

def merge(left,right):
    print(f"merge({left},{right})")

此外，在发布此类问题时，请包含带有确切错误的回溯。它会帮助这里的其他人帮助你。