input: Write a function to create and print a simple blockchain system in Python using the Block class. The function should define a Block class that takes index, timestamp, data, and previous_hash as parameters, along with a hash_block method to generate the hash of the block contents. The function should also include methods to create the blockchain and print it.
  def create_and_print_blockchain():
      # Define the Block class
      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.hash_block()
  
          # Create the hash of the block contents
          def hash_block(self):
              sha = hashlib.sha256()
              sha.update((str(self.index) + 
                          str(self.timestamp) + 
                          str(self.data) + 
                          str(self.previous_hash)).encode('utf-8'))
              return sha.hexdigest()
  
      # Create the blockchain
      def create_blockchain():
          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
  
      # Print the blockchain
      def print_blockchain():
          for block in blockchain:
              block_index = str(block.index)
              block_timestamp = str(block.timestamp)
              block_data = str(block.data)
              block_hash = block.hash
  
  assert create_and_print_blockchain() is not None
output: 
  def create_and_print_blockchain():
      import hashlib
      from datetime import datetime
  
      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.hash_block()
  
          def hash_block(self):
              sha = hashlib.sha256()
              sha.update((str(self.index) + 
                          str(self.timestamp) + 
                          str(self.data) + 
                          str(self.previous_hash)).encode('utf-8'))
              return sha.hexdigest()
  
      def create_genesis_block():
          return Block(0, datetime.now(), "Genesis Block", "0")
  
      def next_block(last_block, data):
          this_index = last_block.index + 1
          this_timestamp = datetime.now()
          this_data = data
          this_hash = last_block.hash
          return Block(this_index, this_timestamp, this_data, this_hash)
  
      blockchain_transactions = ["Transaction1", "Transaction2", "Transaction3"]
  
      blockchain = [create_genesis_block()]
      previous_block = blockchain[0]
  
      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
  
      for block in blockchain:
          block_index = str(block.index)
          block_timestamp = str(block.timestamp)
          block_data = str(block.data)
          block_hash = block.hash
  