Fix logging of a single non-serializable object

examples/serialize.py

@@ -11,12 +11,20 @@
 
 
 class CustomClass:
-    """Dummy class to demo logging."""
+    """Dummy class without __str__ method to demo logging."""
 
     def __init__(self, value):
         """Initialize CustomClass object."""
         self._value = value
 
+
+class CustomClassConvertable():
+    """Dummy class with __str__ method to demo logging."""
+
+    def __init__(self, value):
+        """Initialize CustomClassConvertable object."""
+        self._value = value
+
     def __str__(self):
         """Convert CustomClass to string."""
         return "CustomClass: {}".format(self._value)
@@ -61,7 +69,8 @@ def main():
     logger.info("Test log with multiple str parameters: %s %s",
                 "test1", "test2")
 
-    custom_object = CustomClass('test')
+    custom_object = CustomClassConvertable('test')
+    # formatting uses __repr__ if __str__ method isn't available
     logger.info("Test logging of custom obj: %s", custom_object)
     # log record will contain the following values:
     # args: <__main__.CustomClass object at 0x7f3147041c88>
@@ -79,6 +88,12 @@ def main():
         "custom_field_json": {"a": "test", "b": "test"}
     })
 
+    # logging single object without formatting
+    custom_object_with_str = CustomClassConvertable('test w/ str method')
+    logger.info(custom_object_with_str)  # object has __str__ method
+    custom_object_wo_str = CustomClass('test w/o str method')
+    logger.info(custom_object_wo_str)  # str() will use repr()
+
 
 if __name__ == '__main__':
     main()

kafka_logger/handlers.py

@@ -161,6 +161,10 @@ def prepare_record_dict(self, record):
                     # but it is not 1:1 - logging "inf" float
                     # causes _jsonparsefailure error in ELK
                     value = tuple(repr(arg) for arg in value)
+                if key == "msg" and not isinstance(value, basestring):
+                    # msg contains custom class object
+                    # if there is no formatting in the logging call
+                    value = str(value)
                 rec[key] = "" if value is None else value
 
         return rec