¶ Simple BlockChain Project
In this section, we’re going to build a simple blockchain-like application with Python and Flask to create a voting system. This project is a replica of a blockchain running on a single server and aims to demonstrate key blockchain concepts, such as block creation, linking, and validation. While it mimics some aspects of a blockchain, it does not incorporate full decentralization, consensus mechanisms, or immutability features of a true blockchain system.
If you wanna apply full decentralization, consensus mechanisms, or immutability features checkout Section 4.
This application will display each vote as a new block in a chain, and we’ll validate the blockchain structure to ensure its integrity. This is a simplified version of a blockchain, created for educational purposes, and is designed to help you understand how basic blockchain elements work in a controlled, single-server environment.
Let’s break down each part to make it easy to follow.
¶ Course Outline
- Setup and Requirements
- Understanding the Blockchain Structure
- Building the
BlockandBlockChainClasses - Creating the Flask Web App (
app.py) - Designing the HTML Template (
index.html) - Running the Application
- Testing the Blockchain Voting System
¶ 1. Setup and Requirements
You need Python and Flask installed. Open a terminal and install Flask with:
pip install flask
¶ Folder Structure
Create a folder for your project, and within it, set up the following structure:
project/
├── app.py # Main Flask application
├── PyChain.py # Blockchain classes (Block and BlockChain)
└── templates/
└── index.html # HTML template with Bootstrap
¶ 2. Understanding the Blockchain Structure
A blockchain is a linked list of blocks, each block containing:
- Data (e.g., a vote)
- Previous hash (linking to the previous block)
- Current hash (unique identifier for the block’s contents)
Each new vote will create a new block linked to the previous one, making it tamper-resistant.
¶ 3. Building the Block and BlockChain Classes (PyChain.py)
Here, we define two classes, Block and BlockChain.
# PyChain.py
import hashlib, time
class Block:
def __init__(self, data, prev_hash=""):
self.data = data
self.prev_hash = prev_hash
self.timestamp = time.time()
self.hash = self.calc_hash()
def calc_hash(self):
return hashlib.sha256((str(self.data) + self.prev_hash + str(self.timestamp)).encode()).hexdigest()
class BlockChain:
def __init__(self):
self.chain = [self.create_genesis()]
def create_genesis(self):
return Block("Genesis")
def addBlock(self, block):
block.prev_hash = self.chain[-1].hash
block.hash = block.calc_hash()
self.chain.append(block)
def chainValid(self):
for i in range(1, len(self.chain)):
b, pb = self.chain[i], self.chain[i - 1]
if b.hash != b.calc_hash() or b.prev_hash != pb.hash:
return False
return True
¶ Explanation
-
Block Class:
__init__: Initializes the block with data, a timestamp, and calculates its hash.calc_hash: Generates a SHA-256 hash from the block’s contents.
-
BlockChain Class:
- Initializes a list starting with a "genesis" block (the first block).
addBlock: Links the new block to the previous block.chainValid: Checks the integrity of the blockchain by verifying each block’s hash.
¶ 4. Creating the Flask Web App (app.py)
This file handles the web server and routes for the application.
# app.py
from flask import Flask, render_template, request, redirect
from PyChain import BlockChain, Block
app = Flask(__name__)
chain = BlockChain()
@app.route('/')
def index():
return render_template('index.html', chain=chain.chain, valid=chain.chainValid())
@app.route('/vote', methods=['POST'])
def vote():
choice = request.form.get('choice')
if choice:
chain.addBlock(Block(choice))
return redirect('/')
if __name__ == "__main__":
app.run(debug=True)
¶ Explanation
indexRoute: Loads the main voting page and displays the blockchain status.voteRoute: Receives vote submissions from the form and adds them as new blocks.
¶ 5. Designing the HTML Template (templates/index.html)
This HTML page will display the voting form and blockchain status.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css" rel="stylesheet">
<title>Blockchain Voting</title>
</head>
<body>
<div class="container mt-5">
<h1 class="text-center">Blockchain Voting System</h1>
<div class="card mt-4">
<div class="card-body">
<form method="POST" action="/vote">
<label for="choice" class="form-label">Select your choice:</label>
<select class="form-select mb-3" name="choice" required>
<option value="Candidate 1">Candidate 1</option>
<option value="Candidate 2">Candidate 2</option>
<option value="Candidate 3">Candidate 3</option>
</select>
<button type="submit" class="btn btn-primary">Vote</button>
</form>
</div>
</div>
<h2 class="mt-5">Blockchain Status</h2>
<p>Blockchain Valid: {{ 'Yes' if valid else 'No' }}</p>
<ul class="list-group">
{% for block in chain %}
<li class="list-group-item">
<strong>Block {{ loop.index }}</strong><br>
Data: {{ block.data }}<br>
Hash: {{ block.hash }}<br>
Previous Hash: {{ block.prev_hash }}<br>
Timestamp: {{ block.timestamp }}
</li>
{% endfor %}
</ul>
</div>
</body>
</html>
¶ Explanation
- Form: Dropdown list for selecting a candidate and submitting a vote.
- Blockchain Display: Shows each block’s data, hash, and previous hash.
¶ 6. Running the Application
To run the application:
-
In the terminal, navigate to your project folder.
-
Start the Flask server by running:
python app.py -
Open your browser and go to
http://127.0.0.1:5000/.
You’ll see the voting interface with the blockchain status below.
¶ 7. Testing the Blockchain Voting System
- Vote Submission: Select a candidate and submit your vote.
- Blockchain Display: Each new vote will appear as a block in the blockchain.
- Validation Check: The "Blockchain Valid" indicator will show if all blocks are correctly linked.
¶ Preview of the App
Congratulations! You’ve built a simple blockchain-based voting app with Python.
This project will demonstrate the core concept of blockchain and how blocks are linked together securely.