From fbb1827d84163b9b98dee0afc6e7b832b9f9469a Mon Sep 17 00:00:00 2001
From: Jiaming Yuan <jm.yuan@outlook.com>
Date: Tue, 7 Feb 2023 02:00:45 +0800
Subject: [PATCH] Cleanup booster param types.

---
 python-package/xgboost/_typing.py |  2 +-
 python-package/xgboost/core.py    | 33 +++++++++++--------------------
 2 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/python-package/xgboost/_typing.py b/python-package/xgboost/_typing.py
index 11cd6321dac6..0adad9478770 100644
--- a/python-package/xgboost/_typing.py
+++ b/python-package/xgboost/_typing.py
@@ -25,7 +25,7 @@
 FeatureInfo = Sequence[str]
 FeatureNames = FeatureInfo
 FeatureTypes = FeatureInfo
-BoosterParam = Union[List, Dict]  # better be sequence
+BoosterParam = Union[List, Dict[str, Any]]  # better be sequence
 
 ArrayLike = Any
 PathLike = Union[str, os.PathLike]
diff --git a/python-package/xgboost/core.py b/python-package/xgboost/core.py
index ff33a684255a..f3b986e93210 100644
--- a/python-package/xgboost/core.py
+++ b/python-package/xgboost/core.py
@@ -1655,27 +1655,18 @@ def _transform_interaction_constraints(
 
     def _configure_constraints(self, params: BoosterParam) -> BoosterParam:
         if isinstance(params, dict):
-            value = params.get("monotone_constraints")
-            if value is not None:
-                params["monotone_constraints"] = self._transform_monotone_constrains(
-                    value
-                )
-
-            value = params.get("interaction_constraints")
-            if value is not None:
-                params[
-                    "interaction_constraints"
-                ] = self._transform_interaction_constraints(value)
-        elif isinstance(params, list):
-            for idx, param in enumerate(params):
-                name, value = param
-                if not value:
-                    continue
-
-                if name == "monotone_constraints":
-                    params[idx] = (name, self._transform_monotone_constrains(value))
-                elif name == "interaction_constraints":
-                    params[idx] = (name, self._transform_interaction_constraints(value))
+            # we must use list in the internal code as there can be multiple metrics
+            # with the same parameter name `eval_metric` (same key for dictionary).
+            params = list(params.items())
+        for idx, param in enumerate(params):
+            name, value = param
+            if value is None:
+                continue
+
+            if name == "monotone_constraints":
+                params[idx] = (name, self._transform_monotone_constrains(value))
+            elif name == "interaction_constraints":
+                params[idx] = (name, self._transform_interaction_constraints(value))
 
         return params