How Blockchain Works

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# Block structure
{
    index: 0,
    timestamp: 1700000000,
    data: "Genesis Block",
    previous_hash: "0",
    nonce: 0,
    hash: "0000abc..."
}

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import hashlib
import json

class Block:
    def __init__(self, index, data, previous_hash):
        self.index = index
        self.data = data
        self.previous_hash = previous_hash
        self.hash = self.calculate_hash()

    def calculate_hash(self):
        content = json.dumps({
            "index": self.index,
            "data": self.data,
            "previous": self.previous_hash
        })
        return hashlib.sha256(content.encode()).hexdigest()

# Create blockchain
chain = [
    Block(0, "Genesis Block", "0"),
    Block(1, "Transaction: Alice->Bob", chain[0].hash),
]

for block in chain:
    print(f"Block {block.index}: {block.hash[:16]}...")