Added some comments about message state

kafka/consumer.py

@@ -365,6 +365,13 @@ class SimpleConsumer(Consumer):
             next_offset = None
             for message in resp.messages:
                 next_offset = message.offset
+
+                # update the offset before the message is yielded. This is
+                # so that the consumer state is not lost in certain cases.
+                # For eg: the message is yielded and consumed by the caller,
+                # but the caller does not come back into the generator again.
+                # The message will be consumed but the status will not be
+                # updated in the consumer
                 self.offsets[partition] = message.offset
                 yield message
             if next_offset is None: