input: Write a function to build a simple blockchain system in Python. It should include a Block class with attributes for index, timestamp, data, previous_hash, and hash. Additionally, it should have a method to create the blockchain and another to print the blockchain.
  
  
  def build_blockchain():
      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, "01/01/2023", "Genesis Block", "0")
  
      def next_block(last_block, data):
          this_index = last_block.index + 1
          this_timestamp = "01/01/2023"  # Placeholder timestamp
          this_data = data
          this_hash = last_block.hash
          return Block(this_index, this_timestamp, this_data, this_hash)
  
      blockchain_transactions = ["Tx1", "Tx2", "Tx3"]
  
      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
  
      return blockchain
  
  assert build_blockchain() != []
  assert len(build_blockchain()) == 4
  assert build_blockchain()[0].index == 0
  assert build_blockchain()[1].previous_hash == build_blockchain()[0].hash
  
output: def build_blockchain():
      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, "01/01/2023", "Genesis Block", "0")
  
      def next_block(last_block, data):
          this_index = last_block.index + 1
          this_timestamp = "01/01/2023"  # Placeholder timestamp
          this_data = data
          this_hash = last_block.hash
          return Block(this_index, this_timestamp, this_data, this_hash)
  
      blockchain_transactions = ["Tx1", "Tx2", "Tx3"]
  
      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
  
      return blockchain