Added ability to customise JSON dictionary

Author: svisser

src/jsonlogger.py

@@ -85,11 +85,27 @@ def parse(self):
         standard_formatters = re.compile(r'\((.+?)\)', re.IGNORECASE)
         return standard_formatters.findall(self._fmt)
 
+    def add_fields(self, log_record, record, message_dict):
+        """
+        Override this method to implement custom logic for adding fields.
+        """
+        for field in self._required_fields:
+            log_record[field] = record.__dict__.get(field)
+        log_record.update(message_dict)
+        merge_record_extra(record, log_record, reserved=self._skip_fields)
+
+    def process_log_record(self, log_record):
+        """
+        Override this method to implement custom logic
+        on the possibly ordered dictionary.
+        """
+        return log_record
+
     def format(self, record):
         """Formats a log record and serializes to json"""
-        extras = {}
+        message_dict = {}
         if isinstance(record.msg, dict):
-            extras = record.msg
+            message_dict = record.msg
             record.message = None
         else:
             record.message = record.getMessage()
@@ -102,10 +118,8 @@ def format(self, record):
         except NameError:
             log_record = {}
 
-        for field in self._required_fields:
-            log_record[field] = record.__dict__.get(field)
-        log_record.update(extras)
-        merge_record_extra(record, log_record, reserved=self._skip_fields)
+        self.add_fields(log_record, record, message_dict)
+        self.process_log_record(log_record)
 
         return "%s%s" % (self.prefix,
                          json.dumps(log_record,

tests/tests.py

@@ -141,6 +141,17 @@ def custom(o):
         self.assertEqual(logJson.get("adate"), "very custom")
         self.assertEqual(logJson.get("normal"), "value")
 
+    def testJsonCustomLogicAddsField(self):
+        class CustomJsonFormatter(jsonlogger.JsonFormatter):
+
+            def process_log_record(self, log_record):
+                log_record["custom"] = "value"
+
+        self.logHandler.setFormatter(CustomJsonFormatter())
+        self.logger.info("message")
+        logJson = json.loads(self.buffer.getvalue())
+        self.assertEqual(logJson.get("custom"), "value")
+
 
 if __name__ == '__main__':
     if len(sys.argv[1:]) > 0: