Learn to Build a Blockchain Application in Python

Blockchain Application

Have you ever heard of blockchain application? Well, if you didn’t, you surely are living under a rock.

The blockchain is currently transforming every industry. That’s why, in today’s tutorial, we will learn how to build a blockchain application using Python.

Building A blockchain application in Python

To get started, we first need to define the use of our application. Let’s stick to building a blockchain application that allows users to share stories using blockchain. As we will be using blockchain, there will be added benefits including immutability, unhackable system, and persistence.

The structure of the data that we are aiming is as below.


These are the three minimum entities we need to create in the blockchain. You canadd more entities if you need. Also, to store the data, we will be using JSON. JSON is a popular way of storing information. Below is an example of how a sample data will look like.

Note: – Through the tutorial, we will use both “data” and “transaction” interchangeably. If we say that we need to store transaction into the block, then it means “data” as well.

Block Code

The block code for the above-mentioned entities should be as simple as below.

Making The Block Immutable

As we already know that blockchain is immutable. To achieve immutability, we need to use hash functions in our blockchain app. So, how exactly a hash function work?

Hash functions takes data as an input and produce fixed size data as output. This way, it can be used to validate data. It compute the data and then comes out with a hash value. If the input data is manipulated, the hash value will change. Also, the hash function is easy to compute and is completely secured, it is not possible to guess the input using the hash value.

Let’s write the hash function for our blockchain application.

Building the blockchain

The blockchain is composed of blocks and chain. Also, we need to store them and access them easily. To do so, we will be using Python list. A list is a data type and should work for solving the problem at hand. In later part of the tutorial, we will also write code to make blocks immutable, giving immutability to the whole blockchain.

Every blockchain has its first block which is known as genesis block. Without the genesis block, it is impossible to create the blockchain. A good analogous example to the genesis block is the seed. Without it, the tree just cannot grow.

To build the blockchain, we will create a new Blockchain class.

Proof of Work algorithm

With our simple blockchain created, it’s now time to protect our genesis block. We don’t want anyone to alter it or start a new fresh blockchain by providing new hash information or altering the genesis block. To do so, we need to implement a proof of work algorithm. A proof of work algorithm simply makes sure that no one can change the hash. The algorithm will add some constraints to the hashes generated on the blockchain, making it impossible for anyone to make any change.

To do so, we can add a nonce to our block field. This will ensure that our hash maintains the constraint. If you are still confused, read this amazing article on proof of work by Aleksandr Bulkin.

Now, let’s write the proof of work method. It should be within the Blockchain class.

Adding Blocks to the Chain

After implementing Proof of Work, it’s now time to add blocks. Also, before we add, we need to verify if the POW (proff of work) is working or not. Let’s do it below.

Note: The below code will be added to Blockchain Class.

Last Step: Mining
Our last step is to set up mining method in our blockchain. As we are using Proof of Work algorithm, we need to do block mining. The mining method will also ensure that the miners get something in reward while validating transactions in the blockchain.

The below methods will be included in the Blockchain class.

Conclusion: –
That’s it. We have successfully created a blockchain application. To create the interface, you need to use the Flask framework. This aspect of the tutorial is beyond the scope, and that’s why we will not cover it here By going through the tutorial, you should be able to implement basic blockchain. From here you can do a lot of things and improve the application as much as you can.


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