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Bug: idempotency payloads with set, frozenset or bytes fields cannot be hashed #8725
Description
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Expected Behaviour
A dataclass or Pydantic payload with set, frozenset or bytes fields can be used as the idempotency payload; the key hash is computed deterministically.
Current Behaviour
_IdempotencyKeyEncoder in persistence/base.py handles Enum, date/time, UUID and PurePath only. A set field makes the key computation fail with IdempotencyPersistenceLayerError: Failed to save in progress record to idempotency store - Object of type set is not JSON serializable, which reads like a store outage rather than an unsupported payload.
Code snippet
from dataclasses import dataclass
from aws_lambda_powertools.utilities.idempotency import idempotent_function
@dataclass
class Payload:
id: int
tags: set
@idempotent_function(data_keyword_argument="payload", persistence_store=layer)
def process(payload: Payload):
return "ok"
process(payload=Payload(1, {"a"})) # IdempotencyPersistenceLayerError ... Object of type set is not JSON serializablePossible Solution
Extend _IdempotencyKeyEncoder.default: encode set/frozenset as a sorted list (sort by repr when elements are not comparable) and bytes as base64. Add tests asserting that the same payload with the same set in a different insertion order produces the same key, and that bytes works.
Item 8 of the Idempotency audit in #8603. No AWS resources needed.
Powertools for AWS Lambda (Python) version
latest
AWS Lambda function runtime
3.13
Packaging format used
PyPi
Debugging logs
No response
Activity
Neeraj111010 commentedon Oct 31, 2026
HI @leandrodamascena
I would like to claim this issue! I'll work on extending
_IdempotencyKeyEncoderto supportset,frozenset, andbytes, and add the requested unit tests.leandrodamascena commentedon Nov 1, 2026
@Neeraj111010 it's yours, assigning you now. Go ahead with the PR, and say in the description how you ran the tests.
Neeraj111010 commentedon Nov 1, 2026
Hi @leandrodamascena! Just wanted to drop a quick note that I've got everything wrapped up here. All 33 tests are passing cleanly and lint checks are completely clear.
Thanks again!
anishsinghhh3-bit commentedon Nov 2, 2026
I would like to work on this issue.
leandrodamascena commentedon Nov 2, 2026
Thanks @anishsinghhh3-bit, this one is already assigned to @Neeraj111010. The Logger audit in #8730 becomes issues this week, keep an eye on it.
fix(idempotency): add deterministic support for set, frozenset, and b…
powertools-for-aws-oss-automation commentedon Nov 14, 2026
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