-Python-Blockchain-

import hashlib import time

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

def calculate_hash(self):
    block_string = f"{self.index}{self.previous_hash}{self.timestamp}{self.transactions}".encode()
    return hashlib.sha256(block_string).hexdigest()

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

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

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

class Transaction: def init(self, sender, recipient, amount): self.sender = sender self.recipient = recipient self.amount = amount

def __repr__(self):
    return f"{self.sender} -> {self.recipient}: {self.amount}"

Example usage

if name == "main": my_blockchain = Blockchain()

# Add some transactions
transaction1 = Transaction("Alice", "Bob", 50)
transaction2 = Transaction("Bob", "Charlie", 25)

# Add the first block
block1 = Block(1, my_blockchain.get_latest_block().hash, [transaction1])
my_blockchain.add_block(block1)

# Add the second block
block2 = Block(2, my_blockchain.get_latest_block().hash, [transaction2])
my_blockchain.add_block(block2)

# Output the blockchain
for block in my_blockchain.chain:
    print(f"Block {block.index}:")
    print(f"Previous Hash: {block.previous_hash}")
    print(f"Transactions: {block.transactions}")
    print(f"Hash: {block.hash}")
    print("-" * 20)

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