input: 
  def create_genesis_block():
      """ Create the first block in the blockchain (genesis block):
      >>> genesis_block = create_genesis_block()
      >>> genesis_block.index == 0
      True
      >>> genesis_block.previous_hash == '0'
      True
      """
  
output:     class Block:
          def __init__(self, index, previous_hash, data):
              self.index = index
              self.previous_hash = previous_hash
              self.data = data
              self.hash = self.calculate_hash()
  
          def calculate_hash(self):
              return str(self.index) + self.previous_hash + self.data
  
      return Block(0, '0', 'Genesis Block')