title: design issue with composition in python
body: <p>I am writing a program for parking lot. my <code>ParkingFloor</code> class has <code>ParkingDisplayBoard</code> to show how many spots are free. <code>ParkingDisplayBoard</code> instance creation inside <code>ParkingFloor</code> does not allow independently create  <code>ParkingDisplayBoard</code> object outside and I am bound to call <code>parking_display()</code> method from outer class of <code>ParkingFloor</code> to display spots. Which does not look good as ideally <code>ParkingDisplayBoard</code> should have show responsibly.</p>
  <p>for this I need to remove the &quot;has a&quot; relationship between <code>ParkingFloor</code> and <code>ParkingDisplayBoard</code> which is also not good as per OOPS design as every parking floor must have one and only one display board.</p>
  <p>do you have any other design and python implementation to elegantly solve this design issue?</p>
  <pre><code>class ParkingFloor:
      def __init__(self, name):
          self.name = name
          self.handicapped_spots = 'handicapped spots list'
          self.display_board = ParkingDisplayBoard(self.handicapped_spots)   &lt;-------- this one
  
      def display(self):
          self.display_board.parking_display()
  
  
  class ParkingDisplayBoard:
      def __init__(self, hs):
          self.hs = hs
  
      def parking_display(self):
          print(self.hs)
  
  
  obj = ParkingFloor('First Floor')
  obj.display()
  </code></pre>