Python and Blockchain: Building a Blockchain Explorer

Introduction
Prerequisites
Setup
Creating a Blockchain
Building a Blockchain Explorer
Conclusion

Introduction

In this tutorial, we will explore how to build a Blockchain Explorer using Python. A Blockchain is a decentralized and secure digital ledger that records transactions across multiple computers. A Blockchain Explorer allows us to view and analyze the contents of a Blockchain.

By the end of this tutorial, you will have a basic understanding of Blockchain technology and how to use Python to build a Blockchain Explorer. We will use the Flask framework to create a web-based interface for exploring the Blockchain.

Prerequisites

Before starting this tutorial, you should have a basic understanding of Python programming language and web development concepts. Familiarity with Flask framework will be beneficial. You will also need to have Python and Flask installed on your machine.

Setup

Install Python: Visit the Python Downloads page and download the latest version of Python for your operating system. Follow the installation instructions to complete the setup.
Install Flask: Open a terminal or command prompt and use the following command to install Flask using pip, the Python package installer.
```
pip install flask
```
Now that we have completed the setup, let’s move on to creating a Blockchain.

Creating a Blockchain

To build a Blockchain, we need to define classes for Block and Blockchain. Each Block in a Blockchain contains a data payload, timestamp, previous block hash, and its own hash. ```python import hashlib import datetime

class Block:
    def __init__(self, index, data, previous_hash):
        self.index = index
        self.timestamp = str(datetime.datetime.now())
        self.data = data
        self.previous_hash = previous_hash
        self.hash = self.calculate_hash()

    def calculate_hash(self):
        data = str(self.index) + self.timestamp + str(self.data) + str(self.previous_hash)
        return hashlib.sha256(data.encode()).hexdigest()


class Blockchain:
    def __init__(self):
        self.chain = [self.create_genesis_block()]

    def create_genesis_block(self):
        return Block(0, "Genesis Block", "0")

    def get_latest_block(self):
        return self.chain[-1]

    def add_block(self, data):
        previous_hash = self.get_latest_block().hash
        new_block = Block(len(self.chain), data, previous_hash)
        self.chain.append(new_block)

    def is_chain_valid(self):
        for i in range(1, len(self.chain)):
            current_block = self.chain[i]
            previous_block = self.chain[i - 1]
            if current_block.hash != current_block.calculate_hash():
                return False
            if current_block.previous_hash != previous_block.hash:
                return False
        return True
``` The `Block` class represents each block in the Blockchain. The `calculate_hash` method computes the hash of the block based on the index, timestamp, data, and previous hash. The `Blockchain` class maintains a list of blocks and provides methods for adding new blocks and validating the chain.

Now that we have our Blockchain defined, let’s move on to building the Blockchain Explorer.

Building a Blockchain Explorer

Create a new Python file named explorer.py.

Import the necessary modules.

from flask import Flask, render_template
from blockchain import Blockchain

Create an instance of the Flask application.
```
app = Flask(__name__)
```
Create a new instance of the Blockchain.
```
blockchain = Blockchain()
```

Define a route for the home page.

@app.route("/")
def home():
    return render_template("index.html", chain=blockchain.chain)

Create an HTML template file named index.html in a new folder named templates. Add the following code to the template.

<!DOCTYPE html>
<html>
<head>
    <title>Blockchain Explorer</title>
</head>
<body>
    <h1>Blockchain Explorer</h1>
    <ul>
           
    </ul>
</body>
</html>

Run the Flask application.
```
python explorer.py
```
You should see a message indicating that the application is running on http://localhost:5000.
Open a web browser and navigate to http://localhost:5000 to view the Blockchain Explorer. It will display the blocks in the Blockchain along with their details.

Congratulations! You have successfully built a Blockchain Explorer using Python and Flask. You can further enhance the explorer by adding functionalities like transaction details, search/filter options, and more.

Conclusion

In this tutorial, we have learned how to build a Blockchain Explorer using Python and Flask. We started by creating a simple Blockchain with basic block and chain classes. Then, we utilized Flask to create a web-based interface for exploring the Blockchain. We also covered the process of rendering data from the Flask application to HTML templates.

Blockchain technology has the potential to revolutionize various industries, and exploring its concepts and building applications like a Blockchain Explorer can help in understanding its functionality. Python’s simplicity and versatility make it a suitable choice for implementing Blockchain-related projects.

Feel free to experiment and enhance the Blockchain Explorer according to your requirements and explore more advanced features of Blockchain technology.

Published: 30 November 2019