删除链接列表中的项目时出现实例错误

Question

我正在制作一个linkedlist，我不得不为我的列表添加一些不同的函数，比如max、min、count和index。我现在要添加一个remove函数，它就是这段代码。你知道吗

def removeItem(self, position):

        ''' removeItem removes a selected, because python has a built in "garbage remover",
        you don't have to physically delete the node, you only have to skip that node link and python will destroy it
        by it self.'''

        currentNode = ListNode
        previousNode = None
        count = 0

        while count != position:
            #This is a quick check to make sure the next node isn't empty.
            if currentNode.link is None:
                print("Position Invalid")
                return None
            previousNode = currentNode
            currentNode = currentNode.link
            count += 1

        #Node.Link should link to the next node in the sequence.
        previousNode.link = currentNode.link
        return currentNode

我基本上只是尝试链接序列中的下一个节点，这样内置的垃圾清除器就会从序列中删除该节点。但是，我收到以下错误消息，我知道这与我的实例有关。你知道吗

C:\Python33\python.exe "C:/Users/koopt_000/Desktop/College/Sophomore Semester 2/Computer Science 231/Chapter4/Test.py"
900
Traceback (most recent call last):
1
  File "C:/Users/koopt_000/Desktop/College/Sophomore Semester 2/Computer Science 231/Chapter4/Test.py", line 17, in <module>
1
    print(linked_list.removeItem(3))
2
  File "C:\Users\koopt_000\Desktop\College\Sophomore Semester 2\Computer Science 231\Chapter4\LinkedList.py", line 199, in removeItem
    if currentNode.link is None:
AttributeError: type object 'ListNode' has no attribute 'link'

Process finished with exit code 1

这是我的测试代码：

from ListNode import ListNode
from LinkedList import LinkedList

node1 = ListNode(1)
node2 = ListNode(900)
node3 = ListNode(3)
node4 = ListNode(99)
node1.link = node2
node2.link = node3
node3.link = node4

linked_list = LinkedList((1, 900, 3, 99))
print(linked_list.__max__())
print(linked_list.__min__())
print(linked_list.getCount(900))
print(linked_list.getIndex(3))
print(linked_list.removeItem(3))

这是我的ListNode类的代码：

# ListNode.py
class ListNode(object):

    def __init__(self, item = None, link = None):

        '''creates a ListNode with the specified data value and link
        post: creates a ListNode with the specified data value and link'''

        self.item = item
        self.link = link

这是我的LinkedList类的代码：

from ListNode import ListNode

class LinkedList(object):

    #--------------------------------------------------------------

    def __init__(self, seq=()):

        """ Pre: Creates a Linked List
        Post: Creates a list containing the items in the seq=()"""

        if seq == ():

            # If there is no items to be put into the list, then it creates an empty one.
            self.head = None

        else:

            # Creates a node for the first item.
            self.head = ListNode(seq[0], None)

            # If there are remaining items, then they're added while keeping track of the last node.
            last = self.head
            for item in seq[1:]:
                last.link = ListNode(item, None)
                last = last.link

        self.size = len(seq)

    #-------------------------------------------------------------

    def __len__(self):

        '''Pre: Nothing.
           Post: Returns the number of items in the list.'''

        return self.size

    #-------------------------------------------------------------
    def __max__(self):

        ''' Goes through each node and compares what the max is for the linked list.
        Post: Finds the max of the linked list and returns that value.'''

        if self.head is None:
        return None
        max_value = self.head.item
        node = self.head.link

        while node is not None:
            if node.item > max_value:
                max_value = node.item
            node = node.link
        return max_value

    #--------------------------------------------------------------

    def __min__(self):

        ''' Goes through each node and compares what the min is for the linked list.
        Post: Finds the min of the linked list and returns that value.'''

        if self.head is None:
            return None
        min_value = self.head.item
        node = self.head.link

        while node is not None:
            if node.item < min_value:
                min_value = node.item
            node = node.link
        return min_value

    #--------------------------------------------------------------

    def getCount(self, yourData):

        ''' This function counts the amount of times a certain item is in the Linked List.'''

        count = 0
        node = self.head

        for i in range(self.size):
            data = node.item
            if data is yourData:
                count += 1
            node = node.link
        return count

    #--------------------------------------------------------------

    def getIndex(self, yourData):

        ''' getIndex finds the index of the selected item and returns that value. '''

        node = self.head

        if node is None:
            return None

        for i in range(self.size):
            data = node.item
            if data == yourData:
                return i
            node = node.link

        raise IndexError


    #--------------------------------------------------------------

    def removeItem(self, position):

        ''' removeItem removes a selected, because python has a built in "garbage remover",
        you don't have to physically delete the node, you only have to skip that node link and python will destroy it
        by it self.'''

        currentNode = ListNode
        previousNode = None
        count = 0

        while count != position:
            #This is a quick check to make sure the next node isn't empty.
            if currentNode.link == None:
                print("Position Invalid")
                return None
            previousNode = currentNode
            currentNode = currentNode.link
            count += 1

        #Node.Link should link to the next node in the sequence.
        previousNode.link = currentNode.link
        return currentNode

    #--------------------------------------------------------------

如果有人能帮我找出removeItem函数不起作用的原因，那会很有帮助的！你知道吗

另一方面，我也在尝试创建这个列表的双链接列表，我知道我需要在ListNode函数中添加一个prev\u node函数，但是我还需要添加什么呢？再次感谢！你知道吗