input: def create_blockchain() -> Blockchain:
      """Create a basic blockchain in Python using only the core modules. 
      Return an instance of the Blockchain class.
      """
output:     class Block:
          def __init__(self, index, previous_hash, timestamp, data, hash):
              self.index = index
              self.previous_hash = previous_hash
              self.timestamp = timestamp
              self.data = data
              self.hash = hash
  
      class Blockchain:
          def __init__(self):
              self.chain = [self.create_genesis_block()]
  
          def create_genesis_block(self):
              return Block(0, "0", time.time(), "Genesis Block", self.calculate_hash(0, "0", time.time(), "Genesis Block"))
  
          def calculate_hash(self, index, previous_hash, timestamp, data):
              value = str(index) + previous_hash + str(timestamp) + data
              return hashlib.sha256(value.encode('utf-8')).hexdigest()
  
          def add_block(self, data):
              previous_block = self.chain[-1]
              index = previous_block.index + 1
              timestamp = time.time()
              hash = self.calculate_hash(index, previous_block.hash, timestamp, data)
              new_block = Block(index, previous_block.hash, timestamp, data, hash)
              self.chain.append(new_block)
  
      return Blockchain()