Prevent errors if no formatter is provided

This mimics CPython logging functionality.

Fixes #2

Author: thatbudakguy

mqlog/__init__.py

@@ -3,6 +3,8 @@
 import asyncio
 import logging
 
+_default_formatter = logging.Formatter(logging._default_fmt)
+
 
 class MqttHandler(logging.Handler):
     """
@@ -59,6 +61,11 @@ def emit(self, record):
         if self._should_flush(record):
             self.will_flush.set()
 
+    # Override Handler.format to prevent errors if there's no formatter set
+    def format(self, record):
+        fmt = self.formatter or _default_formatter
+        return fmt.format(record)
+
     # Named with an underscore to avoid conflict with logging.Handler.flush
     async def _flush(self):
         if self.buffer:

tests/test_handler.py

@@ -26,6 +26,11 @@ def setUp(self):
         self.logger.addHandler(self.handler)
         self.logger.setLevel(logging.INFO)
 
+    def test_default_formatter(self):
+        """Handler should use default formatter if none is set"""
+        self.handler.setFormatter(None)
+        self.logger.info("Test message")  # Would error if no formatter
+
     def test_no_flush(self):
         """Buffer should not be flushed until capacity/level reached"""
         self.handler.flush_level = logging.WARNING