Protect a booking invariant
See this course’s project requirements
An original library-room booking simulation using independent objects, invariants, composition and an event history.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- A room-state contract with 10:00 mapped to 3.
- An independent-instance check with unchanged B.
- A rejection record with unchanged booking state.
- A composed booking trace with no event for an unknown room.
- A composition design note with responsibility boundaries.
- A tested booking model with independent state and honest rejection evidence.
Review and revise
Use these criteria to check your work and choose what to improve.
- The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
- Normal, boundary and rejected cases are recorded with expected versus observed results.
- The changed case has a correct explanation and does not rely on hidden state.
- The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Want more background?
The idea in everyday life
A has 10:00→3. Attempt 2 at 10:00, then 5 at 11:00; both violate a stated rule.
Validate before mutation. If a request is rejected, leave existing state unchanged. Strictly checking type excludes Booleans, which Python otherwise treats as integer-like values.
Protect a booking invariant — original worked practice
Validate before mutation. If a request is rejected, leave existing state unchanged. Strictly checking type excludes Booleans, which Python otherwise treats as integer-like values.
A has 10:00→3. Attempt 2 at 10:00, then 5 at 11:00; both violate a stated rule.
1. Step 1
Locate the validation before assignment.
You should see: Party-size and slot checks precede dictionary mutation.
This keeps the rule and its observable result together.
2. Step 2
Attempt the duplicate slot.
You should see: ValueError;10:00 remains 3.
This keeps the rule and its observable result together.
3. Step 3
Attempt the over-capacity request.
You should see: ValueError;11:00 is absent.
This keeps the rule and its observable result together.
4. Step 4
Compare state before and after both failures.
You should see: A rejection record with unchanged booking state.
This keeps the rule and its observable result together.
What to finish
A rejection record with unchanged booking state.
Watch for this
Updating a booking before checking capacity or slot availability, leaving changed state after rejection.
How can I tell I understand it?
Explain and demonstrate the required distinction: Validate before mutation. If a request is rejected, leave existing state unchanged. Strictly checking type excludes Booleans, which Python otherwise treats as integer-like values. Show a changed input and the expected result without weakening this contract.
Quick knowledge check
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Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
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