input: Write a function to create a simple blockchain system in Python. The function should define a Block class with properties like index, timestamp, data, and previous_hash. The function should also include methods to hash the block contents and create the blockchain. Finally, the function should include a method to print the blockchain.
  assert create_blockchain==[create_genesis_block()]
  assert print_blockchain==[block_index, block_timestamp, block_data, block_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()
  
  def create_genesis_block():
      return Block(0, time.time(), "Genesis Block", "0")
  
  def create_blockchain():
      return [create_genesis_block()]
  
  def print_blockchain(blockchain):
      for block in blockchain:
          print(f"Index: {block.index}, Timestamp: {block.timestamp}, Data: {block.data}, Hash: {block.hash}")