פיתוח בלוקצ'יין בפייתון: הטמעת מטבע הקריפטו הראשון שלך

            \nimport hashlib\nimport json\nfrom time import time\nfrom urllib.parse import urlparse\nimport uuid\nimport requests\n
            

              
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            \nclass Block:\n    def __init__(self, index, timestamp, transactions, previous_hash):\n        self.index = index\n        self.timestamp = timestamp\n        self.transactions = transactions\n        self.previous_hash = previous_hash\n        self.hash = self.calculate_hash()\n\n    def calculate_hash(self):\n        block_string = json.dumps({\n            "index": self.index,\n            "timestamp": self.timestamp,\n            "transactions": self.transactions,\n            "previous_hash": self.previous_hash\n        }, sort_keys=True).encode()\n        return hashlib.sha256(block_string).hexdigest()\n
            

              
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            \nclass Blockchain:\n    def __init__(self):\n        self.chain = []\n        self.current_transactions = []\n        # Create the genesis block\n        self.new_block(previous_hash='1', index=0) # Genesis block has index 0\n\n    def new_block(self, previous_hash=None, index=None):\n        # Creates a new Block and adds it to the chain\n        block = Block(index or len(self.chain) + 1,\n                      time(),\n                      self.current_transactions,\n                      previous_hash or self.hash(self.chain[-1]))\n\n        # Reset current transactions\n        self.current_transactions = []\n        self.chain.append(block)\n        return block\n\n    def new_transaction(self, sender, recipient, amount):\n        # Adds a new transaction to the list of transactions for the next block\n        self.current_transactions.append({\n            'sender': sender,\n            'recipient': recipient,\n            'amount': amount,\n        })\n        return self.last_block['index'] + 1\n\n    def hash(self, block):\n        # Hashes a block\n        block_string = json.dumps({\n            "index": block.index,\n            "timestamp": block.timestamp,\n            "transactions": block.transactions,\n            "previous_hash": block.previous_hash\n        }, sort_keys=True).encode()\n        return hashlib.sha256(block_string).hexdigest()\n\n    @property\n    def last_block(self):\n        # Returns the last Block in the chain\n        return self.chain[-1]\n
            

              
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            \nfrom flask import Flask, jsonify, request\n\napp = Flask(__name__)\n\n# Generate a unique node identifier\nnode_identifier = str(uuid.uuid4()).replace('-', '')\n\n# Instantiate the Blockchain\nblockchain = Blockchain()\n\n@app.route('/mine', methods=['GET'])\ndef mine():\n    # We need to add a new transaction to reward the miner\n    # For simplicity, let's assume a hardcoded reward transaction\n    # In a real crypto, this would be more complex (e.g., from a special address)\n    blockchain.new_transaction(sender="0", recipient=node_identifier, amount=1)\n\n    # Forge the new Block\n    previous_block = blockchain.last_block\n    previous_hash = blockchain.hash(previous_block)\n    index = len(blockchain.chain) + 1\n    block = blockchain.new_block(index=index, previous_hash=previous_hash)\n\n    response = {\n        'message': "New Block Forged",\n        'index': block.index,\n        'transactions': block.transactions,\n        'hash': block.hash,\n    }\n    return jsonify(response), 200\n\n@app.route('/transactions/new', methods=['POST'])\ndef new_transaction():\n    values = request.get_json()\n\n    # Check that the required fields are in the POST's JSON data\n    required = ['sender', 'recipient', 'amount']\n    if not all(k in values for k in required):\n        return 'Missing values', 400\n\n    # Create a new transaction\n    index = blockchain.new_transaction(values['sender'], values['recipient'], values['amount'])\n\n    response = {'message': f'Transaction will be added to Block {index}'}\n    return jsonify(response), 201\n\n@app.route('/chain', methods=['GET'])\ndef full_chain():\n    response = {\n        'chain': [vars(block) for block in blockchain.chain],\n        'length': len(blockchain.chain),\n    }\n    return jsonify(response), 200\n\n@app.route('/nodes/register', methods=['POST'])\ndef register_nodes():\n    values = request.get_json()\n\n    nodes = values.get('nodes')\n    if nodes is None:\n        return "Error: Please supply a valid list of nodes", 400\n\n    for node in nodes:\n        blockchain.register_node(node)\n\n    response = {\n        'message': 'New nodes have been added',\n        'total_nodes': list(blockchain.nodes),\n    }\n    return jsonify(response), 201\n\n@app.route('/nodes/resolve', methods=['GET'])\ndef consensus():\n    # This is a simplified consensus algorithm. In a real blockchain,\n    # this would involve complex logic to find the longest valid chain.\n    # For this example, we'll just resolve conflicts by choosing the longest chain.\n    replaced = blockchain.resolve_conflicts()\n\n    if replaced:\n        response = {\n            'message': 'Our chain was replaced',\n            'new_chain': [vars(block) for block in blockchain.chain],\n        }\n    else:\n        response = {\n            'message': 'Our chain is authoritative',\n        }\n\n    return jsonify(response), 200\n\nif __name__ == '__main__':\n    # To run this, you'd typically run multiple instances on different ports\n    # For example: python your_script.py -p 5000\n    # And then: python your_script.py -p 5001 (and so on)\n    # You would then register nodes with each other.\n    app.run(host='0.0.0.0', port=5000)\n
            

              
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            \nclass Blockchain:\n    def __init__(self):\n        self.chain = []\n        self.current_transactions = []\n        self.new_block(previous_hash='1', index=0) # Genesis block\n        self.nodes = set() # To store our network nodes\n        self.difficulty = 4 # Number of leading zeros required for the hash\n\n    def register_node(self, address):\n        '''Adds a new node to the list of nodes'''\n        parsed_url = urlparse(address)\n        self.nodes.add(parsed_url.netloc)\n\n    def valid_proof(self, last_proof, proof):\n        guess = f'{last_proof}{proof}'.encode()\n        guess_hash = hashlib.sha256(guess).hexdigest()\n        return guess_hash[:self.difficulty] == "0" * self.difficulty\n\n    def proof_of_work(self, last_proof):\n        # Simple Proof of Work Algorithm:\n        # - Find a number p' such that hash(pp') contains leading 4 zeroes,\n        # where p is the previous proof, and p' is a new proof\n        proof = 0\n        while self.valid_proof(last_proof, proof) == False:\n            proof += 1\n        return proof\n\n    def new_block(self, index=None, previous_hash=None, proof=None):\n        # Creates a new Block and adds it to the chain\n        block = Block(index or len(self.chain) + 1,\n                      time(),\n                      self.current_transactions,\n                      previous_hash or self.hash(self.chain[-1]))\n\n        # Proof of Work validation\n        last_block_proof = self.chain[-1].proof if len(self.chain) > 0 else 0\n        if proof is None:\n             proof = self.proof_of_work(last_block_proof)\n\n        block.proof = proof\n        block.hash = self.hash(block)\n\n        # Reset current transactions\n        self.current_transactions = []\n        self.chain.append(block)\n        return block\n\n    def new_transaction(self, sender, recipient, amount):\n        # Adds a new transaction to the list of transactions for the next block\n        # Ensure sender and recipient are not the same to prevent self-transactions\n        if sender == recipient:\n            raise ValueError("Sender and recipient cannot be the same.")\n        # Basic check for valid amount, in a real system, more checks are needed.\n        if not isinstance(amount, (int, float)) or amount <= 0:\n            raise ValueError("Amount must be a positive number.")\n\n        self.current_transactions.append({\n            'sender': sender,\n            'recipient': recipient,\n            'amount': amount,\n        })\n        return self.last_block.index + 1\n\n    def hash(self, block):\n        # Hashes a block, including its proof\n        block_string = json.dumps({\n            "index": block.index,\n            "timestamp": block.timestamp,\n            "transactions": block.transactions,\n            "previous_hash": block.previous_hash,\n            "proof": block.proof\n        }, sort_keys=True).encode()\n        return hashlib.sha256(block_string).hexdigest()\n\n    @property\n    def last_block(self):\n        # Returns the last Block in the chain\n        return self.chain[-1]\n\n    # ... (add the rest of the methods like resolve_conflicts, valid_chain etc. and update Flask routes accordingly)\n
            

              
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            \n@app.route('/mine', methods=['GET'])\ndef mine():\n    # In a real cryptocurrency, the miner would be rewarded here.\n    # For simplicity, we'll add a transaction that rewards the node itself.\n    # The sender "0" is a convention for newly minted coins.\n    blockchain.new_transaction(sender="0", recipient=node_identifier, amount=1) # Reward for mining\n\n    # Get the last block's proof\n    last_block = blockchain.last_block\n    last_proof = last_block.proof\n\n    # Find the next proof through Proof of Work\n    proof = blockchain.proof_of_work(last_proof)\n\n    # Forge the new Block by adding it to the chain\n    previous_hash = blockchain.hash(last_block)\n    block = blockchain.new_block(previous_hash=previous_hash, proof=proof)\n\n    response = {\n        'message': "New Block Forged",\n        'index': block.index,\n        'transactions': block.transactions,\n        'proof': block.proof,\n        'hash': block.hash,\n    }\n    return jsonify(response), 200\n
            

              
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            \n    def register_node(self, address):\n        '''Adds a new node to the list of nodes'''\n        parsed_url = urlparse(address)\n        self.nodes.add(parsed_url.netloc)\n
            

              
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            \n    def valid_chain(self, chain):\n        '''Determine if a given blockchain is valid'''\n        last_block = chain[0]\n        current_index = 1\n\n        while current_index < len(chain):\n            block = chain[current_index]\n            # Check if the block's previous hash is correct\n            if block.previous_hash != self.hash(last_block):\n                return False\n\n            # Check if the Proof of Work is correct\n            if not self.valid_proof(last_block.proof, block.proof):\n                return False\n\n            last_block = block\n            current_index += 1\n\n        return True\n\n    def resolve_conflicts(self):\n        '''\n        This is our consensus algorithm used to resolve conflicts.\n        It chooses the longest valid chain.\n        '''\n        neighbours = self.nodes\n        new_chain = None\n\n        # Grab and verify the chains from all the other nodes\n        for node in neighbours:\n            try:\n                response = requests.get(f'http://{node}/chain')\n\n                if response.status_code == 200:\n                    length = response.json()['length']\n                    chain = response.json()['chain']\n\n                    # Convert received chain data back into Block objects for validation\n                    # (This is a simplification; real systems might have more robust serialization)\n                    parsed_chain = []\n                    for block_data in chain:\n                        # Create a dummy block to hash against previous block\n                        # Note: In a full implementation, you'd reconstruct the Block object\n                        # This simplification assumes the data is directly usable for validation check\n                        # A more robust solution would involve a Block class constructor that takes dict\n                        dummy_block_for_hashing = type('obj', (object,), block_data)()\n                        parsed_chain.append(dummy_block_for_hashing)\n\n                    # Check if the chain is longer and valid\n                    if length > len(self.chain) and self.valid_chain(parsed_chain):\n                        new_chain = parsed_chain\n            except requests.exceptions.RequestException as e:\n                print(f"Error fetching chain from node {node}: {e}")\n                continue # Move to the next node if there's an error\n\n        # Replace our chain if we discovered a new, valid chain longer than ours\n        if new_chain:\n            # Reconstruct the actual chain based on the longest one found.\n            # This part requires careful handling of Block object reconstruction.\n            # For this simplified example, we'll assume the parsed_chain can be directly used.\n            # In a production system, you'd map block_data back to your Block class properly.\n            self.chain = new_chain # This assignment might need careful object mapping\n            return True\n\n        return False\n
            

              
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            \n@app.route('/nodes/resolve', methods=['GET'])\ndef consensus():\n    replaced = blockchain.resolve_conflicts()\n\n    if replaced:\n        response = {\n            'message': 'Our chain was replaced',\n            'chain': [vars(block) for block in blockchain.chain],\n        }\n    else:\n        response = {\n            'message': 'Our chain is authoritative',\n        }\n\n    return jsonify(response), 200\n
            

              
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