code: def get_item_with_id(self, uid):
          
          for item in self.get_items():
              if item.id == uid:
                  return item
  
          return None
docs: Returns item for defined UID.
  
          >>> book.get_item_with_id('image_001')
  
          :Args:
            - uid: UID for the item
  
          :Returns:
            Returns item object. Returns None if nothing was found.