Expose MetricFinalizersType through the tf.learning API.
The change just simplifies workflow for type annotated implementation of the tff.learning.Model interface.
@@ -52,6 +52,7 @@ from tensorflow_federated.python.learning.framework.optimizer_utils import state
from tensorflow_federated.python.learning.keras_utils import federated_aggregate_keras_metric
from tensorflow_federated.python.learning.keras_utils import from_keras_model
from tensorflow_federated.python.learning.model import BatchOutput
+from tensorflow_federated.python.learning.model import MetricFinalizersType
from tensorflow_federated.python.learning.model import Model
from tensorflow_federated.python.learning.model_update_aggregator import compression_aggregator
from tensorflow_federated.python.learning.model_update_aggregator import ddp_secure_aggregator
