Complete section: Start the Blockchain Application

Author: 15Dkatz

block.py

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+import time
+
+from crypto_hash import crypto_hash
+
+class Block:
+    """
+    Block: a unit of storage.
+    Store transactions in a blockchain that supports a cryptocurrency.
+    """
+    def __init__(self, timestamp, last_hash, hash, data):
+        self.timestamp = timestamp
+        self.last_hash = last_hash
+        self.hash = hash
+        self.data = data
+
+    def add_block(self, data):
+        self.chain.append(Block(data))
+
+    def __repr__(self):
+        return (
+            'Block('
+            f'timestamp: {self.timestamp}, '
+            f'last_hash: {self.last_hash}, '
+            f'hash: {self.hash}, '
+            f'data: {self.data})'
+        )
+
+    @staticmethod
+    def mine_block(last_block, data):
+        """
+        Mine a block based on the given last_block and data.
+        """
+        timestamp = time.time_ns()
+        last_hash = last_block.hash
+        hash = crypto_hash(timestamp, last_hash, data)
+
+        return Block(timestamp, last_hash, hash, data)
+
+    @staticmethod
+    def genesis():
+        """
+        Generate the genesis block.
+        """
+        return Block(1, 'genesis_last_hash', 'genesis_hash', [])
+
+
+def main():
+    genesis_block = Block.genesis()
+    block = Block.mine_block(genesis_block, 'foo')
+    print(f'block: {block}')
+
+if __name__ == '__main__':
+    main()

blockchain.py

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+from block import Block
+
+class Blockchain:
+    """
+    Blockchain: a public ledger of transactions.
+    Implemented as a list of blocks - data sets of transactions
+    """
+    def __init__(self):
+        self.chain = [Block.genesis()]
+
+    def add_block(self, data):
+        self.chain.append(Block.mine_block(self.chain[-1], data))
+
+    def __repr__(self):
+        return f'Blockchain: {self.chain}'
+
+def main():
+    blockchain = Blockchain()
+    blockchain.add_block('one')
+    blockchain.add_block('two')
+
+    print(blockchain)
+    print(f'blockchain.py __name__: {__name__}')
+
+if __name__ == '__main__':
+    main()

crypto_hash.py

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+import hashlib
+import json
+
+def crypto_hash(*args):
+    """
+    Return a sha-256 hash of the given arguments.
+    """
+    stringified_args = sorted(map(lambda data: json.dumps(data), args))
+    joined_data = ''.join(stringified_args)
+
+    return hashlib.sha256(joined_data.encode('utf-8')).hexdigest()
+
+def main():
+    print(f"crypto_hash('one', 2, [3]): {crypto_hash('one', 2, [3])}")
+    print(f"crypto_hash(2, 'one', [3]): {crypto_hash(2, 'one', [3])}")
+
+if __name__ == '__main__':
+    main()