fix: add timezone to timestamps

eppo_client/client.py

@@ -222,7 +222,7 @@ def get_assignment_detail(
             "featureFlag": flag_key,
             "variation": result.variation.key if result and result.variation else None,
             "subject": subject_key,
-            "timestamp": datetime.datetime.utcnow().isoformat(),
+            "timestamp": _utcnow().isoformat(),
             "subjectAttributes": subject_attributes,
             "metaData": {"sdkLanguage": "python", "sdkVersion": __version__},
         }
@@ -370,7 +370,7 @@ def evaluate_bandit_action(
                 "modelVersion": (
                     bandit_data.bandit_model_version if evaluation else None
                 ),
-                "timestamp": datetime.datetime.utcnow().isoformat(),
+                "timestamp": _utcnow().isoformat(),
                 "subjectNumericAttributes": (
                     subject_context_attributes.numeric_attributes
                     if evaluation.subject_attributes
@@ -492,3 +492,7 @@ def convert_actions_to_action_contexts(
     actions: Union[ActionContexts, ActionAttributes]
 ) -> ActionContexts:
     return {k: convert_attributes_to_context_attributes(v) for k, v in actions.items()}
+
+
+def _utcnow() -> datetime.datetime:
+    return datetime.datetime.now(datetime.timezone.utc)

test/client_bandit_test.py

@@ -2,6 +2,7 @@
 # making client_test.py too long.
 
 
+import datetime
 import json
 import os
 from time import sleep
@@ -156,6 +157,37 @@ def test_get_bandit_action_bandit_error(mock_bandit_evaluator):
     assert len(mock_assignment_logger.bandit_events) == 0
 
 
+def test_bandit_event_has_utc_timestamp():
+    # tests that allocation filtering based on subject attributes works correctly
+    client = get_instance()
+    actions = {
+        "adidas": ContextAttributes(
+            numeric_attributes={"discount": 0.1},
+            categorical_attributes={"from": "germany"},
+        ),
+        "nike": ContextAttributes(
+            numeric_attributes={"discount": 0.2}, categorical_attributes={"from": "usa"}
+        ),
+    }
+    client.get_bandit_action(
+        "banner_bandit_flag_uk_only",
+        "alice",
+        DEFAULT_SUBJECT_ATTRIBUTES,
+        actions,
+        "default_variation",
+    )
+
+    # testing assignment logger
+    assignment_event = mock_assignment_logger.assignment_events[-1]
+    timestamp = datetime.datetime.fromisoformat(assignment_event["timestamp"])
+    assert timestamp.tzinfo == datetime.timezone.utc
+
+    # testing bandit logger
+    bandit_event = mock_assignment_logger.bandit_events[-1]
+    timestamp = datetime.datetime.fromisoformat(bandit_event["timestamp"])
+    assert timestamp.tzinfo == datetime.timezone.utc
+
+
 def test_get_bandit_action_with_subject_attributes():
     # tests that allocation filtering based on subject attributes works correctly
     client = get_instance()

test/client_test.py

@@ -1,4 +1,5 @@
 import json
+import datetime
 import os
 from time import sleep
 from unittest.mock import patch
@@ -113,6 +114,40 @@ def test_log_assignment(mock_config_requestor, mock_logger):
     assert mock_logger.log_assignment.call_count == 1
 
 
+@patch("eppo_client.assignment_logger.AssignmentLogger")
+@patch("eppo_client.configuration_requestor.ExperimentConfigurationRequestor")
+def test_assignment_event_has_utc_timestamp(mock_config_requestor, mock_logger):
+    flag = Flag(
+        key="flag-key",
+        enabled=True,
+        variation_type=VariationType.STRING,
+        variations={"control": Variation(key="control", value="control")},
+        allocations=[
+            Allocation(
+                key="allocation",
+                splits=[
+                    Split(
+                        variation_key="control",
+                        shards=[Shard(salt="salt", ranges=[Range(start=0, end=10000)])],
+                    )
+                ],
+                do_log=True,
+            )
+        ],
+        total_shards=10_000,
+    )
+
+    mock_config_requestor.get_configuration.return_value = flag
+    client = EppoClient(
+        config_requestor=mock_config_requestor, assignment_logger=mock_logger
+    )
+    client.get_string_assignment("falg-key", "user-1", {}, "default value")
+
+    event = mock_logger.log_assignment.call_args.args[0]
+    timestamp = datetime.datetime.fromisoformat(event["timestamp"])
+    assert timestamp.tzinfo == datetime.timezone.utc
+
+
 @patch("eppo_client.assignment_logger.AssignmentLogger")
 @patch("eppo_client.configuration_requestor.ExperimentConfigurationRequestor")
 def test_get_assignment_handles_logging_exception(mock_config_requestor, mock_logger):