Develop book availability in Python

This is a new feature in an existing application, not a request to regenerate the entire library. Track the change from menu input to observed result.

Lab briefing

[!NOTE] A passing helper is incomplete until the console menu reaches it.

Concepts · First task · Evidence checklist · Reset

Learning objectives

• Define search and availability semantics before implementation.
• Use the actual Python interfaces and import root.
• Connect a tested feature to existing console actions.

Before you start

Prepare 03-python using the common setup and open the copy alone. Run the following commands from its library directory. The bundled feature fixture uses synthetic JSON data.

Concepts and use cases

Search normalizes input for matching, not necessarily for storage. Availability belongs to a book_item, not to every copy of a book. An active loan is one with no return date; a due date in the past does not return it.

Exercise scenario

The librarian requests partial title search and copy-level availability. New loans, reservations, accounts and persistence changes are out of scope.

Task 1 - Inspect the workflow and baseline

python -m unittest discover -s tests -p "test_*.py" -v

1. Record test discovery and results.
2. Read console/common_actions.py, console/console_app.py, the entities, and the JSON repository methods.
3. Ask for a trace of existing patron search and the proposed book-search insertion points. Verify method names against this Python fixture.
4. Inspect how loans are linked to book_item and patron.

Task 2 - Set the contract

Construct these scenarios in tests with controlled dates. Choose result ordering explicitly. Do not claim lower() and casefold() have identical behavior for all Unicode strings; record the normalization you choose for the feature.

Task 3 - Plan before editing

Plan the book-availability feature in the current Python library. Reuse the
existing input loop and repository contracts. Map BOOK-1..6 to tests, distinguish
Book from BookItem, and keep search read-only. Do not implement loans/reservations.

Inspect data access, active-loan joins and menu wiring. A design that joins a loan to a title instead of a copy cannot satisfy BOOK-4.

Task 4 - Implement and test

1. Write the two-copy regression before implementation.
2. Ask Agent to implement one reviewed slice and no unrelated cleanup.
3. Connect the new action to prompt, input mapping and dispatch.
4. Add boundary tests and run the whole small fixture suite.
5. Run python console/main.py and exercise search manually.
6. Compare JSON files before/after search; search must not persist changes.
7. Temporarily treat every past due date as returned. Confirm BOOK-6 fails, then restore the correct implementation.

Verify your work

• The menu reaches the feature.
• Search behavior and ordering are explicit.
• Availability is calculated for each physical copy.
• A negative mutation is detected.
• Borrowing, membership and existing tests remain unchanged.

Troubleshooting

Run from library for imports. Distinguish a no-results response from a loader failure. If the supplied tests all pass before the feature exists, add the missing regression rather than assuming they cover the new behavior.

Independent practice

Add an author filter as a separately specified feature. Preserve existing title normalization and declare how combined filters behave.

Reset

Stop the console, save evidence, and restore only named feature/test files in the disposable copy. Do not change the original data or publish a repository automatically.

Official references

• Python testing
• Context engineering
• Agent planning