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Create an Inventory System with Products Warehouses and Stock Entries

Design an inventory system using composition: Products stored in Warehouses tracked via stock entries. Implement methods to add entities, record stock, transfer items, and query quantities.

Python practice28 minComposition & Real-World ModelingAdvancedLast updated April 11, 2026

Problem statement

Build an Inventory system composed of Product and Warehouse objects. The Inventory should track stock quantities by creating/maintaining stock entries (product + warehouse -> quantity). Implement an API that allows: - Adding products and warehouses. - Recording incoming stock to a specific warehouse. - Transferring stock between warehouses while preserving total quantity. - Querying the quantity of a product in a specific warehouse and the total across all warehouses. Your classes should encourage composition: Inventory contains/manages Products, Warehouses, and the stock bookkeeping. Methods that mutate the inventory (add_product, add_warehouse, stock_product, transfer) should return the Inventory instance to allow method chaining. Query methods should return integers. Be careful to validate inputs: you may assume SKUs and warehouse codes are case-sensitive strings. Transfers should not allow moving more than available in the source warehouse. If a query is made for unknown product or warehouse, return 0 for stock queries.

Task

Model a multi-class inventory system using composition. Practice designing clear APIs for adding products/warehouses, recording stock entries, transferring stock, and querying per-warehouse and total quantities.

Examples

Basic add and stock

Input

Inventory().add_product('SKU1', 'Widget').add_warehouse('W1', 'Main').stock_product('SKU1', 'W1', 100).get_total_stock('SKU1')

Output

100

Create inventory, add product SKU1 and warehouse W1, record 100 units in W1. Total for SKU1 is 100.

Input format

A single expression creating/using the Inventory class. Examples show chaining: Inventory().add_product(...).add_warehouse(...).stock_product(...).get_total_stock(...).

Output format

Query methods return integers. The test harness compares str(returned_value) to the expected string.

Constraints

Do not use external libraries. Methods that change state should return the Inventory instance to support chaining. Query methods must return integers >= 0. Transfers must not allow negative quantities or moving more than available in the source warehouse.

Samples

Sample 1

Input

Inventory().add_product('P','Thing').add_warehouse('A','Alpha').stock_product('P','A',10).get_stock('P','A')

Output

After stocking 10 units of product 'P' in warehouse 'A', get_stock for that warehouse should return 10.