Bug: EventBridgeEvent dataclass has optional fields as compulsory

[amin-farjadi]

Expected Behaviour

replay-name field is optional for event bridge events, that should be reflected in EventBridgeEvent data class.

from aws_lambda_powertools.utilities.data_classes import EventBridgeEvent, event_source


def test_event_bridge_event():

    @event_source(data_class=EventBridgeEvent)
    def lambda_handler(event: EventBridgeEvent, _context):
        source = event.source
        _ = event.account
        return source

    event = {
        "version": "0",
        "id": "6a7e8feb-b491-4cf7-a9f1-bf3703467718",
        "detail-type": "EC2 Instance State-change Notification",
        "source": "aws.ec2",
        "account": "111122223333",
        "time": "2017-12-22T18:43:48Z",
        "region": "us-west-1",
        "resources": [],
        "detail": {
            "instance_id": "i-1234567890abcdef0",
            "state": "terminated",
        },
    }

    source = lambda_handler(event, {})

    assert source == "aws.ec2"

Current Behaviour

The above test rasises KeyError for the replay-name field.

Code snippet

Provided above

Possible Solution

Changed all non-compulsory properties (get_id, version, account, time, region, resources, replay_name) to use self.get() and return str | None (or list[str] | None). The three guaranteed fields (source, detail_type, detail) remain unchanged.

Steps to Reproduce

Run the above test

Powertools for AWS Lambda (Python) version

latest

AWS Lambda function runtime

3.14

Packaging format used

Lambda Layers

Debugging logs

self = <aws_lambda_powertools.utilities.data_classes.event_bridge_event.EventBridgeEvent object at 0x1121cb0e0>
key = 'replay-name'

    def __getitem__(self, key: str) -> Any:
>       return self._data[key]
E       KeyError: 'replay-name'

.venv/lib/python3.14/site-packages/aws_lambda_powertools/utilities/data_classes/common.py:98: KeyError

[leandrodamascena]

Hey @amin-farjadi, thanks for digging into this. I think there are actually two separate things here.

On resources and replay-name you're right, and I can accept a PR for this. Both can be missing from a real event that hits your Lambda: CloudTrail events don't carry resources, and replay-name only shows up on replayed events. So those should return None instead of blowing up.

The others (account, region, time, version, id) I'd rather leave as they are. Those aren't fields you set, EventBridge stamps them on the way through the bus. The minimal source/detail-type/detail shape in the docs is what you hand to PutEvents, not what your function receives. Once a rule actually invokes your Lambda, they're always there. The KeyError you hit is from building the event by hand without them, which won't happen on the real path. If I made them optional, everyone would have to start handling a None that never really occurs.

So pls fix the PR to make resources and replay_name optional and leave the rest as is, ok?

Thanks.

[amin-farjadi]

Hi @leandrodamascena, that's a good point. Will fix by tomorrow, thanks for the quick review.

[amin-farjadi]

Hi @leandrodamascena, I have updated the issue description and PR #8301 to reflect your comment.

I believe resources field always exists in the envelope but, can be an empty list. It is only replay-name that is optional.