Building a Simple Blockchain in Python

Blockchain technology has revolutionized various industries with its decentralized and secure approach to data management. In this tutorial, we’ll dive into building a simple blockchain from scratch using Python, exploring the fundamental concepts that underpin this innovative technology.

Prerequisites

Ensure you have Python installed on your machine.

Implementing a Basic Blockchain

Step 1: Define the Block Class

Create a Python script (e.g., `blockchain.py`) and define the `Block` class representing each block in the blockchain:

import datetime
import hashlib

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

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

Step 2: Create the Blockchain Class

Define the `Blockchain` class to manage the blocks and chain operations:

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

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

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

    def add_block(self, new_block):
        new_block.previous_hash = self.get_latest_block().hash
        new_block.hash = new_block.calculate_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

Step 3: Testing the Blockchain

Instantiate and test the basic blockchain functionality:

# Create a blockchain
my_blockchain = Blockchain()

# Add new blocks
my_blockchain.add_block(Block(1, datetime.datetime.now(), "Transaction Data", ""))
my_blockchain.add_block(Block(2, datetime.datetime.now(), "Another Transaction", ""))

# Check if the blockchain is valid
print("Is blockchain valid?", my_blockchain.is_chain_valid())

# Manipulate the chain (tampering with data)
my_blockchain.chain[1].data = "Manipulated Data"

# Recheck validity after manipulation
print("Is blockchain valid after manipulation?", my_blockchain.is_chain_valid())

Conclusion

Congratulations! You’ve implemented a simple blockchain in Python, demonstrating the core concepts of blocks, hashing, and chain validation. This basic example lays the foundation for understanding more complex blockchain implementations and applications in various domains.