input: 
  def create_blockchain():
      """Compose a basic blockchain system in Python.
      The blockchain should include a Block class representing each block, and a Blockchain class managing the chain of blocks. The Blockchain class should have methods to add a new block and to return the entire blockchain in JSON format.
      >>> blockchain = create_blockchain()
      >>> blockchain.add_block({'timestamp': '2023-10-01', 'data': 'First block data'})
      >>> blockchain.add_block({'timestamp': '2023-10-02', 'data': 'Second block data'})
      >>> blockchain.get_chain()
      '[{"index": 0, "timestamp": "2023-10-01", "data": "First block data", "previous_hash": null, "hash": "<hash>"}, {"index": 1, "timestamp": "2023-10-02", "data": "Second block data", "previous_hash": "<hash>", "hash": "<hash>"}]'
      """
  
output:     
      class Block:
          def __init__(self, index, timestamp, data, previous_hash):
              self.index = index
              self.timestamp = timestamp
              self.data = data
              self.previous_hash = previous_hash
              self.hash = self.calculate_hash()
          
          def calculate_hash(self):
              block_string = f"{self.index}{self.timestamp}{self.data}{self.previous_hash}"
              return hashlib.sha256(block_string.encode()).hexdigest()
  
      class Blockchain:
          def __init__(self):
              self.chain = [self.create_genesis_block()]
          
          def create_genesis_block(self):
              return Block(0, "2023-10-01", "Genesis Block", "0")
          
          def get_latest_block(self):
              return self.chain[-1]
          
          def add_block(self, new_block):
              new_block.index = self.get_latest_block().index + 1
              new_block.previous_hash = self.get_latest_block().hash
              new_block.hash = new_block.calculate_hash()
              self.chain.append(new_block)
          
          def get_chain(self):
              return json.dumps([block.__dict__ for block in self.chain])
  
      return Blockchain()
  