input: def build_simple_blockchain():
      """ Builds a simple blockchain system in Python. 
      
      >>> build_simple_blockchain()
      [Block(0, 'Genesis Block', None, '0')]
      """
output:     
      class Block:
          def __init__(self, index, data, previous_hash, hash):
              self.index = index
              self.data = data
              self.previous_hash = previous_hash
              self.hash = hash
          
          def __repr__(self):
              return f"Block({self.index}, '{self.data}', {self.previous_hash}, '{self.hash}')"
      
      def calculate_hash(index, data, previous_hash):
          import hashlib
          value = str(index) + data + str(previous_hash)
          return hashlib.sha256(value.encode()).hexdigest()
      
      blockchain = []
      genesis_block = Block(0, 'Genesis Block', None, calculate_hash(0, 'Genesis Block', '0'))
      blockchain.append(genesis_block)
      
      return blockchain
  