Bug: DictWrapper should fully implement Mapping interface

[Tankanow]

Expected Behaviour

DictWrapper and all of its subclasses should fully implement the Mapping interface so that it can be used interchangeably with code that expects the event to be a dictionary. This helps Powertools Middleware play nicely with existing middleware.

Current Behaviour

DictWrapper does not implement the abstract __iter__ and __len__ methods from the Mapping interface. Currently, client code cannot iterate over any subclass of DictWrapper, nor can it use the dictionary built-ins keys, values, or items.

Code snippet

from aws_lambda_powertools.utilities.data_classes.common import DictWrapper

event = DictWrapper({'foo': 'bar'})

[k for k in event]  # raises KeyError: 0
# all of the following raise AttributeError: 'DictWrapper' object has no attribute '...'
event.keys()
event.items()
event.values()

Possible Solution

DictWrapper should subclass either Mapping or Dict, for example:

class DictWrapper(Mapping):
    """Provides a single read only access to a wrapper dict"""

    def __init__(self, data: Dict[str, Any]):
        self._data = data

    def __getitem__(self, key: str) -> Any:
        return self._data[key]

    def __eq__(self, other: Any) -> bool:
        if not isinstance(other, DictWrapper):
            return False

        return self._data == other._data

    def get(self, key: str) -> Optional[Any]:
        return self._data.get(key)

    @property
    def raw_event(self) -> Dict[str, Any]:
        """The original raw event dict"""
        return self._data

    # missing methods
    def __iter__(self) -> Iterator:
        return iter(self._data)

    def __len__(self) -> int:
        return len(self._data)

Steps to Reproduce

see comment above

AWS Lambda Powertools for Python version

latest

AWS Lambda function runtime

3.9

Packaging format used

PyPi

Debugging logs

No logs here. I'm happy to submit the PR to fix this. This should be a non-breaking change.

[rubenfonseca]

Hi @Tankanow thank you for the very clear explanation! Would you mind opening a PR with the changes, together with a couple of tests? We will be thrilled to review it and include it in our next release.

[Tankanow]

@rubenfonseca, happy to do so. I'll get to it this week. 👍🏽

[github-actions]

This is now released under 1.30.0 version!