input: def create_blockchain():
      """
      Creates a simple blockchain system in Python. The blockchain is composed of blocks,
      each containing an index, a timestamp, data, and a hash value. The first block
      in the chain is the genesis block, which is created manually. Subsequent blocks
      are added to the chain, each referencing the hash of the previous block.
      
      Example:
      >>> create_blockchain()
      <Blockchain object>
      """
      blockchain = [create_genesis_block()]
      previous_block = blockchain[0]
  
      # Add blocks for each item in the list of transactions
      for i in range(1, len(blockchain_transactions)):
          block_to_add = next_block(previous_block, blockchain_transactions[i])
          blockchain.append(block_to_add)
          previous_block = block_to_add
output:     return blockchain