Implement Assignment Logging (#10)

* implement assignment logger

* fix lint errors

* fix bug

* make subjectAttributes property of assignment event

Author: ploomiz

eppo_client/__init__.py

@@ -37,14 +37,18 @@ def init(config: Config) -> EppoClient:
     config_requestor = ExperimentConfigurationRequestor(
         http_client=http_client, config_store=config_store
     )
+    assignment_logger = config.assignment_logger
     global __client
     global __lock
     try:
         __lock.acquire_write()
         if __client:
             # if a client was already initialized, stop the background processes of the old client
             __client._shutdown()
-        __client = EppoClient(config_requestor=config_requestor)
+        __client = EppoClient(
+            config_requestor=config_requestor,
+            assignment_logger=assignment_logger,
+        )
         return __client
     finally:
         __lock.release_write()

eppo_client/assignment_logger.py

@@ -0,0 +1,6 @@
+from typing import Dict
+
+
+class AssignmentLogger:
+    def log_assignment(self, assignment_event: Dict):
+        pass

eppo_client/client.py

@@ -1,5 +1,8 @@
 import hashlib
+import datetime
+import logging
 from typing import List, Optional
+from eppo_client.assignment_logger import AssignmentLogger
 from eppo_client.configuration_requestor import (
     ExperimentConfigurationDto,
     ExperimentConfigurationRequestor,
@@ -10,10 +13,17 @@
 from eppo_client.shard import get_shard, is_in_shard_range
 from eppo_client.validation import validate_not_blank
 
+logger = logging.getLogger(__name__)
+
 
 class EppoClient:
-    def __init__(self, config_requestor: ExperimentConfigurationRequestor):
+    def __init__(
+        self,
+        config_requestor: ExperimentConfigurationRequestor,
+        assignment_logger: AssignmentLogger = AssignmentLogger(),
+    ):
         self.__config_requestor = config_requestor
+        self.__assignment_logger = assignment_logger
         self.__poller = Poller(
             interval_millis=POLL_INTERVAL_MILLIS,
             jitter_millis=POLL_JITTER_MILLIS,
@@ -53,14 +63,26 @@ def get_assignment(
             "assignment-{}-{}".format(subject_key, experiment_key),
             experiment_config.subject_shards,
         )
-        return next(
+        assigned_variation = next(
             (
                 variation.name
                 for variation in experiment_config.variations
                 if is_in_shard_range(shard, variation.shard_range)
             ),
             None,
         )
+        assignment_event = {
+            "experiment": experiment_key,
+            "variation": assigned_variation,
+            "subject": subject_key,
+            "timestamp": datetime.datetime.utcnow().isoformat(),
+            "subjectAttributes": subject_attributes,
+        }
+        try:
+            self.__assignment_logger.log_assignment(assignment_event)
+        except Exception as e:
+            logger.error("[Eppo SDK] Error logging assignment event: " + str(e))
+        return assigned_variation
 
     def _subject_attributes_satisfy_rules(
         self, subject_attributes: dict, rules: List[Rule]

eppo_client/config.py

@@ -1,3 +1,4 @@
+from eppo_client.assignment_logger import AssignmentLogger
 from eppo_client.base_model import SdkBaseModel
 
 from eppo_client.validation import validate_not_blank
@@ -6,6 +7,11 @@
 class Config(SdkBaseModel):
     api_key: str
     base_url: str = "https://eppo.cloud/api"
+    assignment_logger: AssignmentLogger = AssignmentLogger()
 
     def _validate(self):
         validate_not_blank("api_key", self.api_key)
+
+    class Config:
+        # needed for the AssignmentLogger class which is not of type SdkBaseModel
+        arbitrary_types_allowed = True

test/client_test.py

@@ -82,6 +82,46 @@ def test_assign_subject_not_in_sample(mock_config_requestor):
     assert client.get_assignment("user-1", "experiment-key-1") is None
 
 
+@patch("eppo_client.assignment_logger.AssignmentLogger")
+@patch("eppo_client.configuration_requestor.ExperimentConfigurationRequestor")
+def test_log_assignment(mock_config_requestor, mock_logger):
+    mock_config_requestor.get_configuration.return_value = ExperimentConfigurationDto(
+        subjectShards=10000,
+        percentExposure=100,
+        enabled=True,
+        variations=[
+            VariationDto(name="control", shardRange=ShardRange(start=0, end=10000))
+        ],
+        name="recommendation_algo",
+        overrides=dict(),
+    )
+    client = EppoClient(
+        config_requestor=mock_config_requestor, assignment_logger=mock_logger
+    )
+    assert client.get_assignment("user-1", "experiment-key-1") == "control"
+    assert mock_logger.log_assignment.call_count == 1
+
+
+@patch("eppo_client.assignment_logger.AssignmentLogger")
+@patch("eppo_client.configuration_requestor.ExperimentConfigurationRequestor")
+def test_get_assignment_handles_logging_exception(mock_config_requestor, mock_logger):
+    mock_config_requestor.get_configuration.return_value = ExperimentConfigurationDto(
+        subjectShards=10000,
+        percentExposure=100,
+        enabled=True,
+        variations=[
+            VariationDto(name="control", shardRange=ShardRange(start=0, end=10000))
+        ],
+        name="recommendation_algo",
+        overrides=dict(),
+    )
+    mock_logger.log_assignment.side_effect = ValueError("logging error")
+    client = EppoClient(
+        config_requestor=mock_config_requestor, assignment_logger=mock_logger
+    )
+    assert client.get_assignment("user-1", "experiment-key-1") == "control"
+
+
 @patch("eppo_client.configuration_requestor.ExperimentConfigurationRequestor")
 def test_assign_subject_with_with_attributes_and_rules(mock_config_requestor):
     matches_email_condition = Condition(