input: 
  def compose_basic_blockchain():
      """
      Compose a basic blockchain system in Python that includes classes for blocks and the blockchain itself.
      The Block class should accept an index, timestamp, data, and previous_hash, and compute its own hash.
      The Blockchain class should have a method to add blocks to the chain and a method to return the entire blockchain in JSON format.
      >>> blockchain = compose_basic_blockchain()
      >>> blockchain.add_block({'timestamp': '2023-01-01', 'data': 'Genesis Block'})
      >>> blockchain.add_block({'timestamp': '2023-01-02', 'data': 'First Block'})
      >>> blockchain.get_chain()
      '[{"index": 0, "timestamp": "2023-01-01", "data": "Genesis Block", "previous_hash": null, "hash": "6d77....."}, {"index": 1, "timestamp": "2023-01-02", "data": "First Block", "previous_hash": "6d77......", "hash": "4b9e......"}]'
      """
      import hashlib
      import json
  
      def sha256(data):
          hash_function = hashlib.sha256()
          hash_function.update(data.encode('utf-8'))
          return hash_function.hexdigest()
  
      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 = sha256(f'{self.index}{self.timestamp}{self.data}{self.previous_hash}')
  
      class Blockchain:
          def __init__(self):
              self.chain = []
  
          def add_block(self, data):
              previous_hash = self.chain[-1].hash if len(self.chain) > 0 else None
              block = Block(len(self.chain), data['timestamp'], data['data'], previous_hash)
              self.chain.append(block)
  
          def get_chain(self):
              return json.dumps([b.__dict__ for b in self.chain], indent=2)
      
      return Blockchain()
  
output:     blockchain = Blockchain()
      blockchain.add_block({'timestamp': '2023-01-01', 'data': 'Genesis Block'})
      blockchain.add_block({'timestamp': '2023-01-02', 'data': 'First Block'})
      return blockchain