fix: address code review comments.

docs/decisions/0005-optional-import-of-confluent-kafka.rst

@@ -11,7 +11,7 @@ Context
 
 * `confluent-kafka`_ is a library written and maintained by Confluent, our managed instance provider (see :doc:`0004-kafka-managed-hosting`). The library abstracts out the work for sending and receiving events to and from the Kafka cluster and converting them into message objects.
 * confluent-kafka in turn is a wrapper around a C library called `librdkafka`_ (distributed as `librdkafka_dev`)
-* librdkafka-dev does not currently have a compiled binary available for Linux/aarch64
+* librdkafka-dev does not currently have a compiled binary available for Linux/aarch64, which causes issues for developers who are running Tutor on M1 Macs.
 
 As a result of the points above, if a package includes a dependency on confluent-kafka, developers will not be able to install the package in Linux/aarch64 environments.
 

edx_event_bus_kafka/config.py

@@ -14,10 +14,13 @@
     confluent_kafka = None
 
 
-# return type (Optional[SchemaRegistryClient]) removed for better error messaging when confluent-kafka is not available
 def create_schema_registry_client():
     """
     Create a schema registry client from common settings.
+
+    Returns
+        None if confluent_kafka library is not available or the settings are invalid.
+        SchemaRegistryClient if it is.
     """
     if not confluent_kafka:
         warnings.warn('Library confluent-kafka not available. Cannot create schema registry client.')

edx_event_bus_kafka/consumer/event_consumer.py

@@ -49,19 +49,21 @@ class KafkaEventConsumer:
     """
 
     def __init__(self, topic, group_id, signal):
-        if confluent_kafka:
-            self.topic = topic
-            self.group_id = group_id
-            self.signal = signal
-            self.consumer = self._create_consumer()
-        else:
+        if confluent_kafka is None:
             raise Exception('Library confluent-kafka not available. Cannot create event consumer.')
 
-    # return type (Optional[DeserializingConsumer]) removed for better error messaging when confluent-kafka is not
-    # available
+        self.topic = topic
+        self.group_id = group_id
+        self.signal = signal
+        self.consumer = self._create_consumer()
+
     def _create_consumer(self):
         """
         Create a DeserializingConsumer for events of the given signal instance.
+
+        Returns
+            None if confluent_kafka is not available.
+            DeserializingConsumer if it is.
         """
 
         schema_registry_client = create_schema_registry_client()

edx_event_bus_kafka/publishing/event_producer.py

@@ -124,7 +124,6 @@ def get_serializer(signal: OpenEdxPublicSignal) -> AvroSignalSerializer:
 # outbound-message queue and threads. The use of this cache allows the
 # producers to be long-lived.
 
-# return type (Optional[SerializingProducer]) removed for better error messaging when confluent-kafka is not available
 @lru_cache
 def get_producer_for_signal(signal: OpenEdxPublicSignal, event_key_field: str):
     """
@@ -136,6 +135,9 @@ def get_producer_for_signal(signal: OpenEdxPublicSignal, event_key_field: str):
         signal: The OpenEdxPublicSignal to make a producer for
         event_key_field: Path to the event data field to use as the event key (period-delimited
           string naming the dictionary keys to descend)
+    Returns:
+        None if confluent_kafka is not defined or the settings are invalid.
+        SerializingProducer if it is.
 
     Performance note:
         This could be cached, but requires care such that it allows changes to settings via