CLIENTS-2607: Updated documentation to emphasize the use of logger instead of log_cb (confluentinc#1447)

Updated documentation to reflect the use of logger instead of log_cb. 
Added testcase as well for logger.

Author: pranavrth

docs/index.rst

@@ -720,12 +720,8 @@ providing a dict of configuration properties to the instance constructor, e.g.
   consumer = confluent_kafka.Consumer(conf)
 
 
-The supported configuration values are dictated by the underlying
-librdkafka C library. For the full range of configuration properties
-please consult librdkafka's documentation:
-https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md
-
-The Python bindings also provide some additional configuration properties:
+The Python client provides the following configuration properties in 
+addition to the properties dictated by the underlying librdkafka C library:
 
 * ``default.topic.config``: value is a dict of client topic-level configuration
   properties that are applied to all used topics for the instance. **DEPRECATED:**
@@ -778,3 +774,8 @@ The Python bindings also provide some additional configuration properties:
     mylogger.addHandler(logging.StreamHandler())
     producer = confluent_kafka.Producer({'bootstrap.servers': 'mybroker.com'}, logger=mylogger)
 
+.. note::
+   In the Python client, the ``logger`` configuration property is used for log handler, not ``log_cb``.
+
+For the full range of configuration properties, please consult librdkafka's documentation:
+https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md

tests/test_log.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 
+from io import StringIO
 import confluent_kafka
 import confluent_kafka.avro
 import logging
@@ -114,3 +115,46 @@ def test_logging_constructor():
             p.poll(timeout=0.5)
 
         print('%s: %s: %d log messages seen' % (how, f.name, f.cnt))
+
+
+def test_producer_logger_logging_in_given_format():
+    """Test that asserts that logging is working by matching part of the log message"""
+
+    stringBuffer = StringIO()
+    logger = logging.getLogger('Producer')
+    logger.setLevel(logging.DEBUG)
+    handler = logging.StreamHandler(stringBuffer)
+    handler.setFormatter(logging.Formatter('%(name)s Logger | %(message)s'))
+    logger.addHandler(handler)
+
+    p = confluent_kafka.Producer(
+        {"bootstrap.servers": "test", "logger": logger, "debug": "msg"})
+    val = 1
+    while val > 0:
+        val = p.flush()
+    logMessage = stringBuffer.getvalue().strip()
+    stringBuffer.close()
+    print(logMessage)
+
+    assert "Producer Logger | INIT" in logMessage
+
+
+def test_consumer_logger_logging_in_given_format():
+    """Test that asserts that logging is working by matching part of the log message"""
+
+    stringBuffer = StringIO()
+    logger = logging.getLogger('Consumer')
+    logger.setLevel(logging.DEBUG)
+    handler = logging.StreamHandler(stringBuffer)
+    handler.setFormatter(logging.Formatter('%(name)s Logger | %(message)s'))
+    logger.addHandler(handler)
+
+    c = confluent_kafka.Consumer(
+        {"bootstrap.servers": "test", "group.id": "test", "logger": logger, "debug": "msg"})
+    c.poll(0)
+
+    logMessage = stringBuffer.getvalue().strip()
+    stringBuffer.close()
+    c.close()
+
+    assert "Consumer Logger | INIT" in logMessage