twoline_sequential_sorter.py

def _sequential_ints(self, item_vals):
        return len(item_vals) == len(set(item_vals)) == max(item_vals) - min(item_vals) + 1
        """
                len(item_vals) returns the number of items in the list.
                len(set(item_vals)) returns the unique number of items in the list
                
                If those == then we know there are no dupes in the list.
                
                Lastly, if there are no dupes and the max value minus the min value (+1) 
                equals the len(item_vals), then we know that each int is sequential and that there are no duplicates.
                +1 is added because with:
                [5,6,7,8,9] If you subtract 5 from 9 you'll get 4.  We add one to make sure it equals the length of the list.
        """