input: Write a function to build a simple blockchain system in Python that includes a Block class with attributes for index, timestamp, data, previous_hash, and a method to calculate the block's hash. The function should also include a method to create a blockchain and a method to print the blockchain.
  assert create_blockchain()
  assert print_blockchain()
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()
  
  def create_blockchain():
      blockchain = []
      genesis_block = Block(0, time.time(), "Genesis Block", "0")
      blockchain.append(genesis_block)
      return blockchain
  
  def print_blockchain(blockchain):
      for block in blockchain:
          print(f"Index: {block.index}")
          print(f"Timestamp: {block.timestamp}")
          print(f"Data: {block.data}")
          print(f"Previous Hash: {block.previous_hash}")
          print(f"Hash: {block.hash}")
          print()