old_contents: 
  class TicketOffice(object):
      def __init__(self, trains=None):
          self.trains = trains or {}
      
      def add_train(self, train_id, train):
          self.trains[train_id] = train
  
      def make_reservation(self, reservation_request):
          # TODO: write this code!
          pass
  
  class ReservationRequest(object):
      def __init__(self, train_id, seat_count):
          self.train_id = train_id
          self.seat_count = seat_count
  
  class Reservation(object):
      def __init__(self, train_id, seats=None, booking_reference=None):
          self.train_id = train_id
          self.seats = seats or []
          self.booking_reference = booking_reference
  
  class Train(object):
      def __init__(self, seats=None):
          self.seats = seats or []
  
  class Seat(object):
      def __init__(self, carriage, seat_number):
          self.carriage = carriage
          self.seat_number = seat_number
new_contents: 
  class TicketOffice(object):
      def make_reservation(self, reservation_request):
          # TODO: write this code!
          pass
  
  class ReservationRequest(object):
      def __init__(self, train_id, seat_count):
          self.train_id = train_id
          self.seat_count = seat_count
  
  class Reservation(object):
      def __init__(self, train_id, seats=None, booking_reference=None):
          self.train_id = train_id
          self.seats = seats or []
          self.booking_reference = booking_reference
  
  class Seat(object):
      def __init__(self, carriage, seat_number):
          self.carriage = carriage
          self.seat_number = seat_number
subject: Make the starting code simpler