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Deprecation warning for the Kyber classes #14
Description
From #3: warn the first time someone uses a Kyber* class, once per process, and change nothing else.
- Any
Kyber*entry point (constructor,from_keys, staticencapsulate/decapsulate) warns on first use. Importing doesn't warn - One warning per process total, across all three classes
- The message says Kyber and ML-KEM aren't interoperable (both sides need to switch) and links the migration guide
- Test it in a subprocess: use the classes many times, count exactly one warning; golden vectors still pass
Use a quiet DeprecationWarning for now: a KyberDeprecationWarning subclass, with stacklevel set so it points at the caller's code. Python only shows it by default when it comes from __main__, and that's fine for this release. The README will say it clearly.
Done when: the subprocess test passes and output is unchanged.
Depends on: #13. Plan: WP-6.
Part of #3.
Activity
Zikithezikit commentedon Oct 30, 2026
Handoff for whoever picks this up (#13 is merged; dev-v2 has everything it needs).
Where the entry points are, all in python/pykyber/_kyber.py: for each of Kyber512, Kyber768 and Kyber1024,
__new__,from_keys, and the staticencapsulateanddecapsulate. The methods on the returnedKeypaircome after a constructor orfrom_keyscall that already warned, so they need nothing. Do not touch python/pykyber/_mlkem.py: ML-KEM must never warn, and there is no shared base class with the Kyber classes.Things that will bite:
__main__, and the default per-location registry can swallow repeats. Guard "once per process" with your own module-level flag (take a lock so two threads cannot both warn) instead of relying on the filter, and in the subprocess test run with-W always::DeprecationWarningor-W defaultso you see what is really emitted. Also test that the warning is silent by default for an imported library and that importing pykyber alone emits nothing.__new__, the classmethodfrom_keysand the static methods if you route them through a helper; check it with a test that readswarning.filename.__all__. It is a warning, not an error, so it does not belong in _error.py; a new small module is fine.Not in scope: README and docs (that is #15), version bump, any change to the Kyber behavior.
Zikithezikit commentedon Oct 30, 2026
Done in #38 (rebase-merged into dev-v2 as a666d76 and 6883dd8). First use of any Kyber512/768/1024 entry point emits one KyberDeprecationWarning per process; importing and ML_KEM_* never warn; Kyber output is unchanged (golden vectors pass untouched). The subprocess tests are in python/tests/test_kyber_deprecation.py.
The warning message links https://github.com/Zikithezikit/pykyber/blob/main/docs/migration.md, so #15 has to create exactly docs/migration.md.