Suppose that a company maintains multiple warehouses. Each warehouse stocks various products (not all warehouses stock the same products). The inventory of a product is the amount of any product available at a warehouse. For example, a warehouse in Irvine may stock a brush product, and it may have an inventory of 3 (3 brushes in the Irvine warehouse).

We will represent all this information in a dictionary whose keys are the warehouses: associated with each warehouse is an inner dictionary whose keys are the stocked products (and whose associated values are the inventory of that product in the warehouse). The inventory must always be a non-negative value; an inventory of 0 is legal. For example, a simple/small database might be.

db = {'Irvine' : {'brush': 3, 'comb': 2, 'wallet': 2}, 'Newport': {'comb': 7, 'stapler': 0}, 'Tustin' : {'keychain': 3, 'pencil': 4, 'wallet': 3}}

This data structure means that

1. The Irvine warehouse stocks 3 brushes, 2 combs, and 2 wallets.

2. The Newport warehouse stocks 7 combs, and 0 staplers.

3. The Tustin warehouse stocks 3 keychains, 4 pencils, and 3 wallets.

I have printed this dictionary in an easy to read form. Python prints dictionaries on one line, and can print their key/values in any order, because dictionaries are not ordered. In the following function, do not mutate this dictionary; you can create local data structures in the functions and mutate them as necessary.

(b) The unique_suppler function a dictionary (dict or defaultdict) whose keys are str (the warehouse) and whose associated value is a set of all the products that are stocked only from that warehouse (even if the inventory shown there is 0): for the db dictionary above the result is {'Irvine': {'brush'}, 'Newport': {'stapler'}, 'Tustin': {'keychain', 'pencil'}}