🔒 How can I modify this DLL to support negative indexing?

[austere nymph]

class DoublyLinkedList:
    def __init__(self):
        self.head = self.tail = None

    def appendleft(self, data):
        new_node = ListNode(data)
        if not self.head:
            self.head = self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = self.head = new_node

    def append(self, data):
        new_node = ListNode(data)
        if not self.head:
            self.head = self.tail = new_node
        else:
            new_node.prev = self.tail
            self.tail.next = self.tail = new_node

    def insert(self, data, pos):
        if pos <= 0:
            self.appendleft(data)
        elif pos >= self.index(self.tail.data):
            self.append(data)
        else:
            current = self.head
            index = 0
            while current and index < pos:
                current = current.next
                index += 1
            new_node = ListNode(data)
            new_node.prev, new_node.next = current.prev, current
            current.prev.next = current.prev = new_node

    def index(self, data):
        current = self.head
        index = 0
        while current:
            if current.data == data:
                return index
            current = current.next
            index += 1

    def popleft(self):
        if self.head:
            data = self.head.data
            if self.head == self.tail:
                self.head = self.tail = None
            else:
                self.head, self.head.prev = self.head.next, None
            return data

    def pop(self):
        if self.head:
            data = self.tail.data
            if self.head == self.tail:
                self.head = self.tail = None
            else:
                self.tail, self.tail.next = self.tail.prev, None
            return data```

[molten niche]

@austere nymph

Python help channel opened

Remember to:

• Ask your Python question, not if you can ask or if there's an expert who can help.
• Show a code sample as text (rather than a screenshot) and the error message, if you've got one.
• Explain what you expect to happen and what actually happens.

:warning: Do not pip install anything that isn't related to your question, especially if asked to over DMs.

Closes after a period of inactivity, or when you send !close.

[austere nymph]

    def remove(self, data):
        if self.head:
            current = self.head
            found = False
            while current and not found:
                if current.data == data:
                    if current == self.head:
                        self.popleft()
                    elif current == self.tail:
                        self.pop()
                    else:
                        current.prev.next, current.next.prev = current.next, current.prev
                    found = True
                current = current.next```

[solar flume]

how do you want to add negative indexing

at the insert() function?

[austere nymph]

yeah

[solar flume]

I'm assuming -1 would put it at the end?

[austere nymph]

yeah

[solar flume]

hmm, you'll need to change the behaviour from self.appendleft into something else

oh btw I spotted a bug, elif pos >= self.index(self.tail.data): in insert, if data repeats then the index might be calculated wrongly

[austere nymph]

how do i fix that

[solar flume]

instead of using .index to find the length, just write another method specifically for finding the length

[austere nymph]

as in the number of nodes

[solar flume]

Yeah, number of nodes

[sand oak]

1. When writing your own structures, you should store a length (node count) internally so you don't need to re-calculate it each time. Otherwise, getting the length is very expensive.
2. To change a negative index to a "normal" one, add the negative index to the length of the list.

[austere nymph]

like this? class Node:
def init(self, data):
self.data = data
self.prev = self.next = None

class DoublyLinkedList:
    def __init__(self):
        self.head = self.tail = None

    def __len__(self):
        count = 0
        current = self.head
        while current:
            count += 1
            current = current.next
        return count

    def __getitem__(self, index):
        if index < 0:
            index += len(self)
        if index < 0 or index >= len(self):
            raise IndexError("Index out of range")
        current = self.head
        for _ in range(index):
            current = current.next
        return current.data

    def append(self, data):
        new_node = Node(data)
        if not self.head:
            self.head = self.tail = new_node
        else:
            self.tail.next = new_node
            new_node.prev = self.tail
            self.tail = new_node

    def appendleft(self, data):
        new_node = Node(data)
        if not self.head:
            self.head = self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = self.head = new_node

    def pop(self):
        if not self.tail:
            raise IndexError("List is empty")
        data = self.tail.data
        if self.head == self.tail:
            self.head = self.tail = None
        else:
            self.tail = self.tail.prev
            self.tail.next = None
        return data

    def popleft(self):
        if not self.head:
            raise IndexError("List is empty")
        data = self.head.data
        if self.head == self.tail:
            self.head = self.tail = None
        else:
            self.head = self.head.next
            self.head.prev = None
        return data```

[molten niche]

Python help channel closed

This help channel has been closed and it's no longer possible to send messages here. If your question wasn't answered, feel free to create a new post in #1035199133436354600. To maximize your chances of getting a response, check out this guide on asking good questions.