404 Not Found error when querying PyPI JSON API for package metadata

Goal

Develop a client that can gracefully handle cancellation and timeout scenarios when retrieving package metadata from the PyPI JSON API.

Constraints and Uncertainty

The API returns a 404 Not Found with a JSON body containing "Not found" for non‑existent packages, and a 429 Too many requests when the rate limit (~60 req/min) is exceeded. No timeout header or cancellation signal is exposed; clients must rely on their HTTP library’s timeout or cancellation mechanisms. The lack of a documented cancellation protocol is an open design decision that may be addressed in future releases.

Unresolved Questions

1. Does PyPI provide any recommended pattern for canceling in‑progress requests, or is it entirely left to client libraries?
2. What is the expected behavior when a client times out before receiving a response—should the client treat it as a transient error or a permanent failure?
3. Will future PyPI releases introduce a timeout header or cancellation token to support graceful shutdown of long‑running requests?