Unordered List in Python

Last Updated : 6 Oct, 2025

In Python, there is no built-in data structure specifically called an "unordered list." However, we can implement an unordered list using a linked list which consists of nodes where each node contains a data element and a reference to the next node. Linked lists can be either ordered or unordered based on how elements are inserted and maintained.

Implementing an Unordered List Using a Linked List

Node Class

A typical node in a linked list can be represented as a Python class:

Python 
class Node:
    def __init__(self, data=None):
        self.data = data
        self.next = None
  • Purpose: Represents each element in the linked list.
  • Attributes: data stores the value and next points to the next node.

UnorderedList Class

The UnorderedList class manages the nodes and provides methods to perform various operations on the unordered list. Here's the implementation of the class:

Python 
class UnorderedList:
    def __init__(self):
        self.head = None
  • Purpose: Manages the linked list.
  • Attributes: head points to the first node in the list.

Operations in Unordered List

Now, let's define some key methods for our unordered list:

1. Check if the List is Empty:

To check whether the list is empty, we can simply check if the head of the list is None.

Python 
    def is_empty(self):
        return self.head is None

2. Add an Item:

The add() method adds a new node at the beginning of the list. Since it’s an unordered list, the new node is added without worrying about the order.

Python 
    def add(self, item):
        new_node = Node(item)
        new_node.next = self.head
        self.head = new_node

3. Get the Size of the List:

The size() method counts the number of nodes in the list.

Python 
    def size(self):
        current = self.head
        cnt = 0
        while current:
            cnt += 1
            current = current.next
        return cnt

4. Search for an Item:

The search() method checks if a given item exists in the list.

Python 
    def search(self, item):
        current = self.head
        while current:
            if current.data == item:
                return True
            current = current.next
        return False

5. Remove an Item:

The remove() method removes the first occurrence of a given item from the list.

Python 
    def remove(self, item):
        current = self.head
        previous = None
        while current:
            if current.data == item:
                if previous:
                    previous.next = current.next
                else:
                    self.head = current.next
                return True
            previous = current
            current = current.next
        return False

6. Append an Item:

The append() method adds an item at the end of the list.

Python 
    def append(self, item):
        new_node = Node(item)
        if self.is_empty():
            self.head = new_node
            return
        current = self.head
        while current.next:
            current = current.next
        current.next = new_node

7. Display the List:

The display() method prints all elements in the list.

Python 
    def display(self):
        current = self.head
        while current:
            print(current.data, end=" -> ")
            current = current.next
        print("None")

Using the UnorderedList Class

Here's how you can use the UnorderedList class to perform basic operations:

Python 
ul = UnorderedList()

ul.add(31)
ul.add(77)
ul.add(17)
ul.add(93)
ul.add(26)
ul.add(54)

ul.display()  

print("Size:", ul.size())  

print("Search 93:", ul.search(93)) 
print("Search 100:", ul.search(100))  

ul.remove(93)
ul.display()  

ul.append(100)
ul.display()

Output:

54 -> 26 -> 93 -> 17 -> 77 -> 31 -> None
Size: 6
Search 93: True
Search 100: False
54 -> 26 -> 17 -> 77 -> 31 -> None
54 -> 26 -> 17 -> 77 -> 31 -> 100 -> None

Explanation:

  • add(item): Adds an item at the beginning of the list.
  • size(): Returns the number of items in the list.
  • search(item): Searches for an item and returns True if found, False otherwise.
  • remove(item): Removes the first occurrence of an item from the list.
  • append(item): Appends an item at the end of the list.
  • display(): Displays all elements in the list.

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