Address Aaron's comments

eppo_client/bandit.py

@@ -1,5 +1,7 @@
 from dataclasses import dataclass
+import logging
 from typing import Dict, List, Optional, Tuple
+
 from eppo_client.models import (
     BanditCategoricalAttributeCoefficient,
     BanditCoefficients,
@@ -9,6 +11,13 @@
 from eppo_client.sharders import Sharder
 
 
+logger = logging.getLogger(__name__)
+
+
+class BanditEvaluationError(Exception):
+    pass
+
+
 @dataclass
 class Attributes:
     numeric_attributes: Dict[str, float]
@@ -72,6 +81,9 @@ class BanditResult:
     variation: str
     action: Optional[str]
 
+    def to_string(self) -> str:
+        return coalesce(self.action, self.variation)
+
 
 def null_evaluation(
     flag_key: str, subject_key: str, subject_attributes: Attributes, gamma: float
@@ -176,16 +188,19 @@ def weigh_actions(
         ]
 
         # remaining weight goes to best action
-        remaining_weight = 1.0 - sum(weight for _, weight in weights)
+        remaining_weight = max(0.0, 1.0 - sum(weight for _, weight in weights))
         weights.append((best_action, remaining_weight))
         return weights
 
     def select_action(self, flag_key, subject_key, action_weights) -> Tuple[int, str]:
         # deterministic ordering
         sorted_action_weights = sorted(
             action_weights,
-            key=lambda t: self.sharder.get_shard(
-                f"{flag_key}-{subject_key}-{t[0]}", self.total_shards
+            key=lambda t: (
+                self.sharder.get_shard(
+                    f"{flag_key}-{subject_key}-{t[0]}", self.total_shards
+                ),
+                t[0],  # tie-break using action name
             ),
         )
 
@@ -200,9 +215,9 @@ def select_action(self, flag_key, subject_key, action_weights) -> Tuple[int, str
                 return idx, action_key
 
         # If no action is selected, return the last action (fallback)
-        action_index = len(sorted_action_weights) - 1
-        action_key = sorted_action_weights[action_index][0]
-        return action_index, action_key
+        raise BanditEvaluationError(
+            f"[Eppo SDK] No action selected for {flag_key} {subject_key}"
+        )
 
 
 def score_action(

eppo_client/client.py

@@ -253,6 +253,28 @@ def get_bandit_action(
                           - variation (str): The assignment key indicating the subject's variation.
                           - action (str): The key of the selected action if the subject is part of the bandit.
         """
+        try:
+            return self.get_bandit_action_detail(
+                flag_key,
+                subject_key,
+                subject_attributes,
+                actions_with_contexts,
+                default,
+            )
+        except Exception as e:
+            if self.__is_graceful_mode:
+                logger.error("[Eppo SDK] Error getting bandit action: " + str(e))
+                return BanditResult(default, None)
+            raise e
+
+    def get_bandit_action_detail(
+        self,
+        flag_key: str,
+        subject_key: str,
+        subject_attributes: Attributes,
+        actions_with_contexts: List[ActionContext],
+        default: str,
+    ) -> BanditResult:
         # get experiment assignment
         # ignoring type because Dict[str, str] satisfies Dict[str, str | ...] but mypy does not understand
         variation = self.get_string_assignment(
@@ -292,22 +314,22 @@ def get_bandit_action(
             "subjectNumericAttributes": (
                 subject_attributes.numeric_attributes
                 if evaluation.subject_attributes
-                else None
+                else {}
             ),
             "subjectCategoricalAttributes": (
                 subject_attributes.categorical_attributes
                 if evaluation.subject_attributes
-                else None
+                else {}
             ),
             "actionNumericAttributes": (
                 evaluation.action_attributes.numeric_attributes
                 if evaluation.action_attributes
-                else None
+                else {}
             ),
             "actionCategoricalAttributes": (
                 evaluation.action_attributes.categorical_attributes
                 if evaluation.action_attributes
-                else None
+                else {}
             ),
             "metaData": {"sdkLanguage": "python", "sdkVersion": __version__},
         }

eppo_client/configuration_requestor.py

@@ -56,7 +56,6 @@ def store_bandits(self, bandit_data) -> Dict[str, BanditData]:
             config["banditKey"]: BanditData(**config)
             for config in cast(dict, bandit_data.get("bandits", []))
         }
-        print(bandit_configs)
         self.__bandit_config_store.set_configurations(bandit_configs)
         return bandit_configs
 

test/client_bandit_test.py

@@ -25,7 +25,6 @@
         test_case_dict = json.load(test_case_json)
         test_data.append(test_case_dict)
 
-print(test_data)
 
 MOCK_BASE_URL = "http://localhost:4001/api"
 
@@ -69,8 +68,6 @@ def init_fixture():
         )
     )
     sleep(0.1)  # wait for initialization
-    print(client.get_flag_keys())
-    print(client.get_bandit_keys())
     yield
     client._shutdown()
     httpretty.disable()
@@ -91,7 +88,6 @@ def test_get_bandit_action_bandit_does_not_exist():
         [],
         "default_variation",
     )
-    print(result)
     assert result == BanditResult("default_variation", None)