Fix alias handler

optuna/integration/_lightgbm_tuner/alias.py

@@ -1,9 +1,10 @@
+from __future__ import annotations
+
+from collections.abc import Iterable
 from typing import Any
-from typing import Dict
-from typing import List  # NOQA
 
 
-_ALIAS_GROUP_LIST: List[Dict[str, Any]] = [
+_ALIAS_GROUP_LIST: list[dict[str, Any]] = [
     {"param_name": "bagging_fraction", "alias_names": ["sub_row", "subsample", "bagging"]},
     {"param_name": "learning_rate", "alias_names": ["shrinkage_rate", "eta"]},
     {
@@ -27,7 +28,7 @@
 ]
 
 
-def _handling_alias_parameters(lgbm_params: Dict[str, Any]) -> None:
+def _handling_alias_parameters(lgbm_params: dict[str, Any]) -> None:
     """Handling alias parameters."""
 
     for alias_group in _ALIAS_GROUP_LIST:
@@ -40,7 +41,7 @@ def _handling_alias_parameters(lgbm_params: Dict[str, Any]) -> None:
                 del lgbm_params[alias_name]
 
 
-_ALIAS_METRIC_LIST: List[Dict[str, Any]] = [
+_ALIAS_METRIC_LIST: list[dict[str, Any]] = [
     # The list `alias_names` do not include the `metric_name` itself.
     {
         "metric_name": "ndcg",
@@ -103,18 +104,31 @@ def _handling_alias_parameters(lgbm_params: Dict[str, Any]) -> None:
     },
 ]
 
+_ALIAS_METRIC_MAP: dict[str, str] = {
+    alias_name: canonical_metric["metric_name"]
+    for canonical_metric in _ALIAS_METRIC_LIST
+    for alias_name in canonical_metric["alias_names"]
+}
 
-def _handling_alias_metrics(lgbm_params: Dict[str, Any]) -> None:
-    """Handling alias metrics."""
 
+def _handling_alias_metrics(lgbm_params: dict[str, Any]) -> None:
+    """Handling alias metrics."""
     if "metric" not in lgbm_params.keys():
         return
 
-    for metric in _ALIAS_METRIC_LIST:
-        metric_name = metric["metric_name"]
-        alias_names = metric["alias_names"]
+    if not isinstance(lgbm_params["metric"], (str, Iterable)):
+        raise ValueError(
+            "The `metric` parameter is expected to be a string or an iterable object, but got "
+            f"{type(lgbm_params['metric'])}."
+        )
 
-        for alias_name in alias_names:
-            if lgbm_params["metric"] == alias_name:
-                lgbm_params["metric"] = metric_name
-                break
+    if isinstance(lgbm_params["metric"], str):
+        lgbm_params["metric"] = (
+            _ALIAS_METRIC_MAP.get(lgbm_params["metric"]) or lgbm_params["metric"]
+        )
+        return
+
+    canonical_metrics = []
+    for metric in lgbm_params["metric"]:
+        canonical_metrics.append(_ALIAS_METRIC_MAP.get(metric) or metric)
+    lgbm_params["metric"] = canonical_metrics

tests/integration_tests/lightgbm_tuner_tests/test_alias.py

@@ -81,6 +81,11 @@ def test_handling_alias_parameter() -> None:
         (["auc_mu"], "auc_mu"),
         (["custom", "none", "null", "na"], "custom"),
         ([], None),  # If "metric" not in lgbm_params.keys(): return None.
+        ([["lambdarank"]], ["ndcg"]),
+        (
+            [["lambdarank", "mean_average_precision", "root_mean_squared_error"]],
+            ["ndcg", "map", "rmse"],
+        ),
     ],
 )
 def test_handling_alias_metrics(aliases: List[str], expect: str) -> None:
@@ -93,3 +98,8 @@ def test_handling_alias_metrics(aliases: List[str], expect: str) -> None:
         lgbm_params = {}
         _handling_alias_metrics(lgbm_params)
         assert lgbm_params == {}
+
+
+def test_handling_unexpected_alias_metrics() -> None:
+    with pytest.raises(ValueError):
+        _handling_alias_metrics({"metric": 1})