def _get_instances(cls, collection_name, sample_id):
        """Returns a frame number -> Frame dict containing all in-memory frame
        instances for the specified sample.
        """
        return dict(
            cls._instances.get(collection_name, {}).get(str(sample_id), {})
        )
Returns a frame number -> Frame dict containing all in-memory frame
        instances for the specified sample.
        
fiftyone/core/singletons.py