Creating your own Blockchain Network

# blockchain.py

import json
from hashlib import sha256
from time import time


class Blockchain(object):
    def __init__(self):
        self.chain = []
        self.current_transactions = []
        self.new_block(previous_hash=1, proof=100)

    def proof_of_work(self, last_proof):
        # This method is where you the consensus algorithm is implemented.
        # It takes two parameters including self and last_proof
        proof = 0
        while self.valid_proof(last_proof, proof) is False:
            proof += 1
        return proof

    @staticmethod
    def valid_proof(last_proof, proof):
        # This method validates the block
        guess = f'{last_proof}{proof}'.encode()
        guess_hash = sha256(guess).hexdigest()
        return guess_hash[:4] == "0000"

    def new_block(self, proof, previous_hash=None):
        # This function creates new blocks and then adds to the existing chain
        # This method will contain two parameters proof, previous hash
        block = {
            'index': len(self.chain) + 1,
            'timestamp': time(),
            'proof': proof,
            'previous_hash': previous_hash or self.hash(self.chain[-1]),
            'transactions': []
        }
        # Set the current transaction list to empty.
        self.current_transactions = []
        self.chain.append(block)
        return block

    def new_transaction(self, sender, recipient, amount):
        # This function adds a new transaction to already existing transactions
        # This will create a new transaction which will be sent to the next block.
        # It will contain three variables including sender, recipient and amount
        self.current_transactions.append(
            {
                'sender': sender,
                'recipient': recipient,
                'amount': amount,
            }
        )
        return self.last_block['index'] + 1

    @staticmethod
    def hash(block):
        # Used for hashing a block
        # The follow code will create a SHA - 256 block hash
        # and also ensure that the dictionary is ordered

        # convert this to a dictionary of strings
        new_block = dict()
        for key in block.keys():
            new_block[key] = str(block[key])

        block_string = json.dumps(new_block).encode()
        return sha256(block_string).hexdigest()

    @property
    def last_block(self):
        # Calls and returns the last block of the chain
        return self.chain[-1]

# main.py

from uuid import uuid4
from flask import Flask, request, jsonify
from blockchain import Blockchain

app = Flask(__name__)
node_identifier = str(uuid4()).replace('-', '')

# Initializing blockchain
blockchain = Blockchain()


@app.route('/mine', methods=['GET'])
def mine():
    # Here we make the proof of work algorithm work
    last_block = blockchain.last_block
    last_proof = last_block['proof']
    proof = blockchain.proof_of_work(last_proof)

    # rewarding the miner for his contribution. 0 specifies new coin has been mined
    blockchain.new_transaction(
        sender="0",
        recipient=node_identifier,
        amount=1,
    )

    # now create the new block and add it to the chain
    previous_hash = blockchain.hash(last_block)
    block = blockchain.new_block(proof, previous_hash)

    return jsonify({
        'message': 'The new block has been forged',
        'index': block['index'],
        'transactions': block['transactions'],
        'proof': block['proof'],
        'previous_hash': block['previous_hash']
    }), 200


@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json()
    # Checking if the required data is there or not
    required = ['sender', 'recipient', 'amount']
    if not all(k in values for k in required):
        return 'Missing values', 400

    # creating a new transaction
    index = blockchain.new_transaction(
        values['sender'], values['recipient'], values['amount'])
    return jsonify({
        'message': f'Transaction is scheduled to be added to Block No. {str(index)}'
    }), 201


@app.route('/chain', methods=['GET'])
def full_chain():
    return jsonify({
        'chain': str(blockchain.chain),
        'length': len(blockchain.chain)
    }), 200


if __name__ == '__main__':
    app.run(host="0.0.0.0", port=5000)