If you have heard of stacks and want to implement them in Python but need a bit of help to get started, this tutorial will put you in the right direction. Here, we will discuss some simple steps to implement a Python Stack. But first, let's talk about what a stack is and when it can be used.
What is a Stack?
In Data Structures, data is stored in an efficient manner so that you can access and edit data easily. A Stack is basically a linear collection of objects that stores these items in the form of the Last In First Out or LIFO technique. Stacks use LIFO semantics to insert and delete elements and are referred to as “push” and “pop” respectively in the language of Stack. Pop and push are operations in Stack which help to remove data and add data in Stack respectively. In short, Stacks are data structures that allow us to store and retrieve data in sequential order.
Stacks are different from Queues where the objects are arranged in a First In First Out or FIFO manner which is in stark contrast to LIFO. In the FIFO technique, the first item added is removed first, while in the LIFO technique, the last added item is the first one to be removed, much like adding and removing plates from a stack of such plates arranged one on top of another. Stack allows pop & push operations only from one direction, which is referred to as the “top”. In simple words, Stack allows the addition and deletion of items from the top of the Stack. In contrast to lists and arrays, Stacks do not allow random access to the objects.
When to Use Stacks?
Understanding the use case of Stacks with the help of real-world problems can help us lead a solution-based approach for our data storage problems easily and effectively.
So let us take the example of a Developer who wants to build a word processor. The developer has to incorporate a feature that will allow the users to track their actions from the last word to the word before and so on. This is where using a Stack comes in handy where every action will be stored and backtracking will happen from the last position. As new letters will be entered (inserted) to make a word, it will be considered a ” push” in the stack. Backtracking (deleting) will lead to “popping” from the Stack.
How to Implement Stack in Python?
There are a few options by which you can implement Stack in Python but in this article, you will learn only the simplest ways to do it. For this, you have to focus on using the data structures available in the python library instead of spending time working on your own codes or using third party packages.
Implementing Stack in Python can be done by using the following:
- Built-in “List” data structure in Python
- deque which is a library offering Stack and queue operations in one object
- “queue.LifoQueue” class
Implementing Stack Using the List
The built-in data structure list of Python is one way to use Stack in which you will have to use append() instead of push() in order to add elements to the Stack. The pop() function can be used to remove elements from the Stack as usual following the LIFO order.
There are pros and cons to this type of Stack implementation. While using lists in Python, they are implemented as dynamic arrays within the Stacks. This emphasizes the need to resize the Stack whenever an element is added or removed from it. This is because the storage space allocated is more than what is required, therefore, the need for resizing after adding or removing elements.
The disadvantageous part shows up here in the form of speed issues that might creep up as the Stack grows. Additionally, if the elements in the Stack grow into a size bigger than the block that presently is being held by it, you may need to do some memory allocations which can make the append() calls take much longer time than usual.
Implementing Stack Using “collections.deque”
Using the deque class from the collection module allows us to use append and pop operations on both ends equally, and can be used for both Stacks and queues.
Deque is implemented much like a double-linked list. It is favoured in place of lists as it is efficient and has consistency in the performance of inserting and deleting elements from the Stack.
However, it is to be noted that “collections.deque” cannot be used for randomly adding or removing elements from the middle of the Stack, although it is definitely preferred to a list.
Implementing Stack using the “queue.LifoQueue” Class
The Queue module in Python contains many classes that are useful for parallel computing and while working with multiple threads. This module also contains a LIFO queue. In this module, data is entered using the put() function while removing data from the Queue is done using the get() function.
The functions available in the Queue module are:
- put(item)
- maxsize()
- get()
- empty()
- full()
- put_nowait(item)
- get_nowait()
- qsize()
Takeaway
If you are still here that means you are in a position to use Stacks in Python for your use. I hope that this tutorial could help you understand the different ways to implement Stack in Python. Generally, for the implementation of Stack in Python, lists and deques are used.
Having an idea of Stack implementation in Python will help you solve storage related problems in Python efficiently. To know more about data structures and the various functions, libraries, and modules of Python, you can join KnowledgeHut Python programming certification where you can get certified as a Python coder and learn instantly demonstrable skills that you can use in your quest to build a career as a Python programmer and get hired at the top companies around the world.
