Anthropic·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Apr 2026

Summary

This was a later-stage coding round for a recipe service system, building on top of prior levels. The focus was on adding order cancellation and user history tracking, which sounds straightforward but the edge cases pile up fast.

Questions Asked (2)

Implement a cancel_order function that handles edge cases like cancelling an already-cancelled order, a completed order, or an order that doesn't exist at all.

System DesignAPI & IntegrationsTechnical Trade-offs

Author's notes

I jumped straight into the happy path and the interviewer just sat there quietly until I realized I hadn't said a word about completed orders.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and defining the order states and transitions, then design the function to handle each edge case explicitly with appropriate error handling and idempotency. Discuss trade-offs between different error handling strategies and how to ensure consistency in a distributed system.

Pro tip: Emphasize idempotency and clear error semantics: cancelling an already-cancelled order should be a no-op success, while attempting to cancel a completed order should return a specific error. This shows you understand real-world API design and distributed system challenges.

1. Clarify requirements and state model

Ask questions to understand the order lifecycle (e.g., states like PENDING, CANCELLED, COMPLETED) and the expected behavior for each edge case. Define what 'cancel' means in terms of state transitions and side effects.

2. Design the function signature and error handling

Decide on the return type (e.g., success/failure, error codes) and how to communicate different outcomes. Consider using exceptions or result objects, and ensure errors are descriptive and actionable.

3. Implement edge case handling

Write logic to handle each case: non-existent order (return not found), already cancelled (idempotent success or specific error), completed order (return conflict/error), and valid cancellation (update state, trigger side effects).

4. Address concurrency and consistency

Discuss how to handle concurrent cancellation requests (e.g., using locks, transactions, or optimistic concurrency control) to prevent race conditions and ensure data consistency.

5. Test and validate

Outline test cases for each edge case and normal flow, including unit tests and integration tests. Mention the importance of testing idempotency and error responses.

Key Points to Mention

Idempotency: cancelling an already-cancelled order should not cause an error; it should be a no-op or return success.
Error handling: use appropriate HTTP status codes (e.g., 404 for not found, 409 for conflict) or error types to distinguish between different failure modes.
State machine: model order states and allowed transitions to enforce business rules.
Concurrency control: use database transactions, locks, or versioning to handle simultaneous cancellation requests.
Side effects: consider what happens to related resources (e.g., refunds, inventory) when an order is cancelled.
Observability: log cancellation attempts and outcomes for debugging and auditing.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Implement a track_record function that returns a user's full order history including timestamps and statuses, and handle the case where the user has no orders yet.

Data ModelingAPI & Integrations

Author's notes

Pretty much knew what to do here.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the function signature, data sources, and expected return shape (e.g., list of orders with timestamps and statuses). Then outline a clean implementation that queries the order store, maps records to the response format, and explicitly handles the empty case by returning an empty list or a well-defined empty response. Finish by discussing edge cases, performance, and how you'd test it.

Pro tip: Explicitly call out the empty-state contract (e.g., return [] vs null) and mention pagination or streaming for large histories—this shows you think about API design and real-world scale, not just the happy path.

1. Clarify requirements and contract

Ask about the expected return type, ordering, pagination, and whether 'no orders' should return an empty list, null, or a specific status. Confirm the data source (DB, service, cache) and any auth/ownership checks.

2. Design the data model and query

Define the order record shape (id, timestamp, status, etc.) and write a query that fetches all orders for the user, ordered by timestamp. Consider indexes on user_id and timestamp for performance.

3. Implement the function with empty handling

Write the function to fetch, map, and return the orders. Explicitly handle the no-orders case by returning an empty list (or agreed contract) without errors, and ensure timestamps are serialized consistently (e.g., ISO 8601).

4. Address edge cases and scale

Discuss pagination, large histories, missing/invalid user IDs, and partial failures. Mention caching or streaming if appropriate, and how to keep the API responsive.

5. Test and validate

Outline unit tests for normal, empty, and error cases, plus integration tests against the data store. Mention logging/monitoring for observability.

Key Points to Mention

Explicit empty-state handling: return an empty list (or documented contract) rather than null or an error.
Consistent timestamp format (e.g., ISO 8601 UTC) and status enum/string mapping.
Ordering and pagination strategy for large order histories (e.g., cursor-based pagination).
Database indexing on user_id and timestamp for efficient queries.
Authorization: ensure the caller can only access their own orders.
Testing strategy covering happy path, empty case, and error conditions.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.