Implementasi Blockchain Sederhana di Python

import hashlib
import json
import time

class Block:
    def __init__(self, index, previous_hash, transactions, timestamp=None, nonce=0):
        self.index = index
        self.previous_hash = previous_hash
        self.transactions = transactions
        self.timestamp = timestamp or time.time()
        self.nonce = nonce
        self.hash = self.calculate_hash()

    def calculate_hash(self):
        """Menghitung hash blok berdasarkan atributnya."""
        block_string = json.dumps({
            "index": self.index,
            "previous_hash": self.previous_hash,
            "transactions": self.transactions,
            "timestamp": self.timestamp,
            "nonce": self.nonce
        }, sort_keys=True).encode()
        return hashlib.sha256(block_string).hexdigest()

    def mine_block(self, difficulty):
        """Menambang blok menggunakan Proof of Work (PoW)."""
        target = "0" * difficulty
        while self.hash[:difficulty] != target:
            self.nonce += 1
            self.hash = self.calculate_hash()
        print(f"Block {self.index} mined: {self.hash}")

class Blockchain:
    def __init__(self, difficulty=4):
        self.chain = [self.create_genesis_block()]
        self.pending_transactions = []
        self.difficulty = difficulty

    def create_genesis_block(self):
        """Membuat blok pertama (genesis block)."""
        return Block(0, "0", [], timestamp=time.time())

    def get_latest_block(self):
        """Mengambil blok terakhir dalam blockchain."""
        return self.chain[-1]

    def add_transaction(self, transaction):
        """Menambahkan transaksi ke daftar transaksi tertunda."""
        self.pending_transactions.append(transaction)

    def mine_pending_transactions(self):
        """Menambang transaksi yang tertunda ke dalam blok baru."""
        latest_block = self.get_latest_block()
        new_block = Block(index=latest_block.index + 1,
                          previous_hash=latest_block.hash,
                          transactions=self.pending_transactions)
        new_block.mine_block(self.difficulty)
        self.chain.append(new_block)
        self.pending_transactions = []  # Reset transaksi setelah ditambang

    def is_chain_valid(self):
        """Memeriksa apakah blockchain valid dengan mengecek setiap blok."""
        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

# Contoh penggunaan Blockchain
if __name__ == "__main__":
    blockchain = Blockchain(difficulty=4)

    print("Menambahkan transaksi...")
    blockchain.add_transaction({"from": "Alice", "to": "Bob", "amount": 50})
    blockchain.add_transaction({"from": "Charlie", "to": "Dave", "amount": 25})

    print("Menambang blok baru...")
    blockchain.mine_pending_transactions()

    print("Menambahkan transaksi lain...")
    blockchain.add_transaction({"from": "Eve", "to": "Frank", "amount": 75})
    blockchain.mine_pending_transactions()

    print("\nBlockchain valid:", blockchain.is_chain_valid())

    print("\nBlockchain data:")
    for block in blockchain.chain:
        print(f"Index: {block.index}, Hash: {block.hash}, Transactions: {block.transactions}")

Menambahkan transaksi...
Menambang blok baru...
Block 1 mined: 000062fcb96025a85a4a579eb28f0c72d90ab1a7b8da90fbf3b9f1b9ada4c6b5
Menambahkan transaksi lain...
Block 2 mined: 0000c4ca488ad816acb3965eadd23449ac4cbcb8608a08d4802672d51b7de583