old_contents: import sys
  from linguine.transaction_exception import TransactionException
  from linguine.ops.no_op import NoOp
  
  def get_operation_handler(operation):
      if operation in globals():
          constructor = globals()[operation]
          return constructor()
      else:
          raise TransactionException("The requested operation does not exist.")
  
new_contents: import sys
  from linguine.transaction_exception import TransactionException
  from linguine.ops.tfidf import Tfidf
  from linguine.ops.no_op import NoOp
  
  def get_operation_handler(operation):
      if operation == 'tfidf':
          return Tfidf()
      else:
          raise TransactionException("The requested operation does not exist.")
  
subject: fix bug in operation builder