The product_locations function returns a list of 2-tuples: the first index in the 2-tuple is a product name; the second index is another list of 2-tuples: (warehouse, inventory). in the outermost list, the products appear in increasing alphabetical order; in each inner list (for each product) the warehouses appear in increasing alphabetical order: for the db dictionary above the result is[('brush', [('irvine', 3)'comb', [('irvine', 2), ('newport', 7)]), ('keychain', [('tustin', 3)'pencil', [('tustin', 4)'stapler', [('newport', 0)'wallet', [('irvine', 2), ('tustin', 3)]) ]