Manchester | 25-SDC-Nov | Rahwa Haile | Sprint 2 | Implement a linked list in Python

[RahwaZeslusHaile]

Manchester | 25-SDC-Nov | Rahwa Haile | Sprint 2 | Implement a linked list in Python

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Implement a Doubly-Linked List in Python

Description

Implemented a complete doubly-linked list data structure with O(1) worst-case time complexity for all required operations.

Changes

• Created Node class with pointers to next and previous nodes
• Created LinkedList class with efficient head/tail management
• Implemented three core operations with guaranteed O(1) performance:
  • push_head(): Insert element at list head, returns handle for later removal
  • pop_tail(): Remove and return element from list end
  • remove(): Remove any element given its handle, without list traversal

Please review my work — thank you!

[cjyuan]

The code in linked_list_test.py expects both .next and .previous properties of the removed node to be assigned None. Currently your implementation could not pass all the tests.

Note: Do you know the why it is a good practice to assign .next and .previous of the removed node to None?

[cjyuan]

Could consider delegating this task to remove() -- less code to maintain.

[RahwaZeslusHaile]

@cjyuan I appreciate the explanation about why it is a good practice to assign .next and .previous good practice—it makes sense for memory management, preventing accidental traversal, and making debugging easier.

[cjyuan]

The code in linked_list_test.py expects both .next and .previous properties of the removed node to be assigned None.
Can you ensure your implementation meet this expectation?

The tests in linked_list_test.py is not quite complete. Here' is a test I added, which your implementation could not pass:

    def test_remove_middle(self):
        l = LinkedList()
        l.push_head("a")
        b = l.push_head("b")
        l.push_head("c")

        l.remove(b)

        self.assertIsNone(b.next)
        self.assertIsNone(b.previous)

        self.assertEqual(l.pop_tail(), "a")
        self.assertEqual(l.pop_tail(), "c")

[RahwaZeslusHaile]

Thanks for the feedback @cjyuan ! I've updated the implementation to set .next and .previous to None after removal.

[cjyuan]

I don't see any new commits on this PR branch.

[RahwaZeslusHaile]

Sorry @cjyuan I pushed it now

[cjyuan]

There is still only 1 commit on this PR branch.

You have two "linked list" branches on your repo. Did you push your change on this branch?

[RahwaZeslusHaile]

Sorry @cjyuan for the confusion now the changes are updated

[cjyuan]

Changes look good!

[cjyuan]

ChatGPT suggests this:

Using repr(v) is the conventional approach inside __repr__.

Seems reasonable but I did not verify it.