Add type annotations for mlengine_operator_utils (#10297)

Add type annotations, including a few changes to ensure the right types
are passed through. Specifically, if region is not given, it must be
provided in the DAG's default_args.

airflow/providers/google/cloud/utils/mlengine_operator_utils.py

@@ -24,31 +24,35 @@
 import json
 import os
 import re
+from typing import Callable, Dict, Iterable, List, Optional, Tuple, TypeVar
 from urllib.parse import urlsplit
 
 import dill
 
+from airflow import DAG
 from airflow.exceptions import AirflowException
 from airflow.operators.python import PythonOperator
 from airflow.providers.google.cloud.hooks.gcs import GCSHook
 from airflow.providers.google.cloud.operators.dataflow import DataflowCreatePythonJobOperator
 from airflow.providers.google.cloud.operators.mlengine import MLEngineStartBatchPredictionJobOperator
 
-
-def create_evaluate_ops(task_prefix,  # pylint: disable=too-many-arguments
-                        data_format,
-                        input_paths,
-                        prediction_path,
-                        metric_fn_and_keys,
-                        validate_fn,
-                        batch_prediction_job_id=None,
-                        project_id=None,
-                        region=None,
-                        dataflow_options=None,
-                        model_uri=None,
-                        model_name=None,
-                        version_name=None,
-                        dag=None,
+T = TypeVar("T", bound=Callable)  # pylint: disable=invalid-name
+
+
+def create_evaluate_ops(task_prefix: str,  # pylint: disable=too-many-arguments
+                        data_format: str,
+                        input_paths: List[str],
+                        prediction_path: str,
+                        metric_fn_and_keys: Tuple[T, Iterable[str]],
+                        validate_fn: T,
+                        batch_prediction_job_id: Optional[str] = None,
+                        region: Optional[str] = None,
+                        project_id: Optional[str] = None,
+                        dataflow_options: Optional[Dict] = None,
+                        model_uri: Optional[str] = None,
+                        model_name: Optional[str] = None,
+                        version_name: Optional[str] = None,
+                        dag: Optional[DAG] = None,
                         py_interpreter="python3"):
     """
     Creates Operators needed for model evaluation and returns.
@@ -186,6 +190,9 @@ def validate_err_and_count(summary):
     :rtype: tuple(DataFlowPythonOperator, DataFlowPythonOperator,
                   PythonOperator)
     """
+    batch_prediction_job_id = batch_prediction_job_id or ""
+    dataflow_options = dataflow_options or {}
+    region = region or ""
 
     # Verify that task_prefix doesn't have any special characters except hyphen
     # '-', which is the only allowed non-alphanumeric character by Dataflow.
@@ -203,7 +210,7 @@ def validate_err_and_count(summary):
     if dag is not None and dag.default_args is not None:
         default_args = dag.default_args
         project_id = project_id or default_args.get('project_id')
-        region = region or default_args.get('region')
+        region = region or default_args['region']
         model_name = model_name or default_args.get('model_name')
         version_name = version_name or default_args.get('version_name')
         dataflow_options = dataflow_options or \