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vinayak
vinayak

Posted on • Originally published at itsvinayak.hashnode.dev on

How To Build A Blockchain In Python

#python #blockchain #python3 #build

Blockchain is a shared, immutable ledger that simplifies the method of recording transactions and tracking assets in a network. It's a constantly growing list of records known as a block. These blocks are connected, creating a chain known as a blockchain.

The fundamental feature of blockchain :

  • Immutable and Unhackable records

  • Distributed ledger technology

  • Persistent in storing data (no loss of data)

Setting up Virtualenv & Installing Dependencies 🔌

create a virtualenv, using python's built-in module called venv. Here env is the name of the environment.

python3 -m venv env
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for activating this virtualenv, we need to source it.

source ./env/bin/activate
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Installing Dependencies

we need flask as a dependency for serving our blockchain

pip install Flask==2.2.2
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Setting up Folder Structure 🗂

  • create a base folder, and name it blockchain

  • inside this folder create a file called blockchain.py which will hold our blockchain code.

  • create another file called server.py this will contain our server code, to server our blockchain.

Creating a Blockchain

Import Dependencies 

 import datetime import json import hashlib import time
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Now, create a class called blockchain , which will hold all our logic and chain itself. Inside this blockchain class, we will have some functions.

  • init : initialize the blockchain, and creates a Genius Block 
 def __init__ (self) -> None: """ initialize the blockchain """ self.chain = [] # create the genesis block self.create_block(proof=1, previous_hash="0")
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  • create_block : this function creates a new block and adds it to the blockchain, it takes proof and the previous hash as an argument 
 def create_block(self, proof, previous_hash): """ add a new block to the blockchain """ block = {} block["index"] = len(self.chain) + 1 block["timestamp"] = str(datetime.datetime.now()) block["proof"] = proof block["previous_hash"] = previous_hash self.chain.append(block) return block
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  • get_previous_block : This function gets the previous block, which is added to the blockchain 
 def get_previous_block(self): """ get the previous block """ return self.chain[-1]
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  • proof_of_work : proof of work is a Consensus Protocol in blockchain used to define finding a number such that the hash of the number, is hard to find because it takes a lot of time, and computing power. 
 def proof_of_work(self, previous_proof): start_time = time.time() new_proof = 1 check_proof = False while check_proof is False: hash_operation = hashlib.sha256( str(new_proof **2 - previous_proof** 2).encode() ).hexdigest() if hash_operation[:4] == "0000": check_proof = True else: new_proof += 1 elapsed = time.time() - start_time print(' time take to get new_proof using pow : ', elapsed) return new_proof
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  • hash : hash function takes a block and converts it into hash using sha256 , and returns the hash 
 def hash(self, block) -> str: """ hash the block using sha256, and return the hash """ encoded_block = str(json.dumps(block, sort_keys=True)).encode('utf-8') hash = hashlib.sha256(encoded_block).hexdigest() return hash
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  • is_chain_valid : check if the blockchain is valid 
 def is_chain_valid(self, chain): """ check if the blockchain is valid """ if chain == [] or chain == None: # if the chain is empty or None, then the chain is not passed as a parameter chain = self.chain previous_block = chain[0] block_index = 1 while block_index < len(chain): block = chain[block_index] if block["previous_hash"] != self.hash(previous_block): return False previous_proof = previous_block["proof"] proof = block["proof"] hash_operation = hashlib.sha256( str(proof **2 - previous_proof** 2).encode() ).hexdigest() if hash_operation[:4] != "0000": return False previous_block = block block_index += 1 return True
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Creating a web server

Creating a Flask web server 

import os from flask import Flask, jsonify # env PORT = os.getenv('PORT', 8080) DEBUG = os.getenv('DEBUG', True) app = Flask( __name__ ) @app.route('/', methods=['GET']) def home(): return "<h1>Welcome to the Blockchain</h1>", 200 if __name__ == " __main__": app.run(host="0.0.0.0", port=PORT, debug=DEBUG)
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Importing our blockchain

importing and initializing blockchain will create Genius Block

from blockchain import Blockchain blockchain = Blockchain()
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Adding mine_block function

This mine_block function helps used to mine a block in a given blockchain

@app.route('/mine_block', methods=['GET']) def mine_block(): previous_block = blockchain.get_previous_block() previous_proof = previous_block['proof'] proof = blockchain.proof_of_work(previous_proof) previous_hash = blockchain.hash(previous_block) block = blockchain.create_block(proof, previous_hash) response = {} response['message'] = "Blocked is just mined !!" response['index'] = block['index'] response['timestamp'] = block['timestamp'] response['previous_hash'] = block['previous_hash'] response['proof'] = block['proof'] return jsonify(response), 201
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Adding get_chain function

This get_chain function will return a JSON list of blocks and its attribute.

@app.route('/get_chain', methods=['GET']) def get_chain(): blockchain_clone = blockchain.get_chain() return jsonify(blockchain_clone), 200
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Adding is_valid function

This function checks if the current blockchain Is valid or not

@app.route('/is_valid', methods=['GET']) def is_valid(): is_valid = blockchain.is_chain_valid(blockchain.chain) if is_valid: response = {} response['message'] = "Blockchain is valid" return jsonify(response), 200 else: response = {} response['message'] = "Blockchain is not valid" return jsonify(response), 200
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Starting webserver

To start the web server, we will execute the server.py

python3 server.py
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All codes with docker files are present on GitHub

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