readback

Validation via echo-confirmation. Send a value, read it back through a confirm function, and fail closed on mismatch — the classic command-then-verify pattern used in safety and control systems.

Install

pip install readback

Quickstart

from readback import readback, ReadbackError

sent = {"motor": "arm", "rpm": 1200}
confirmed = readback(sent, confirm_fn=lambda: {"motor": "arm", "rpm": 1200})
assert confirmed == sent

try:
    readback(sent, confirm_fn=lambda: {"motor": "arm", "rpm": 0})
except ReadbackError as e:
    assert e.expected == sent
    assert e.got["rpm"] == 0

Why this exists

• Catch write/read skew before acting on a bad state
• Fail closed with structured expected / got on mismatch
• Zero dependencies; works anywhere Python runs

API

Symbol	Description
readback(value, confirm_fn)	Confirm echo matches; return value
ReadbackError	Mismatch error with .expected and .got

Related packages

Part of the coldbricks micro-library suite (small, typed, zero-dependency helpers):

Package	Role
buzzkill	Guaranteed shutdown callbacks
aftercare	Reverse-order teardown
fluffer	Startup pre-warm
edging	Token-bucket rate limit
readback	Echo-confirmation validation
hearback	Output re-validation decorator
agecheck	Timezone-correct age thresholds
transponder	State broadcast on change

Development

pip install -e ".[dev]"
pytest -q
ruff check .
mypy src

Roadmap

This is an early 0.1.0 release (Alpha) with active development planned:

• Tolerance / partial-match policies
• Async confirm functions
• Structured logging of mismatch traces

License

MIT © Coldbricks — coldbricks@gmail.com