old_contents: class MemoryController():
  
      def power_on(self):
          print("MemoryController.power_on()")
  
new_contents: class MemoryController():
      """Represents a computer system's memory controller."""
  
      def power_on(self):
          """Powers on this memory controller."""
          print("MemoryController.power_on()")
  
subject: Add docstrings to memory module