match CPython behavior w.r.t. default (last resort) logger

Author: vladak

adafruit_logging.py

@@ -246,13 +246,13 @@ def emit(self, record: LogRecord) -> None:
 
 
 logger_cache = {}
+_default_handler = StreamHandler()
 
 
 def _addLogger(logger_name: Hashable) -> None:
     """Adds the logger if it doesn't already exist"""
     if logger_name not in logger_cache:
         new_logger = Logger(logger_name)
-        new_logger.addHandler(StreamHandler())
         logger_cache[logger_name] = new_logger
 
 
@@ -330,15 +330,30 @@ def handle(self, record: LogRecord) -> None:
 
         :param LogRecord record: log record
         """
-        if not self.hasHandlers() and not self.emittedNoHandlerWarning:
-            sys.stderr.write(f"Logger '{self.name}' has no handlers\n")
+        if (
+            _default_handler is None
+            and not self.hasHandlers()
+            and not self.emittedNoHandlerWarning
+        ):
+            sys.stderr.write(
+                f"Logger '{self.name}' has no handlers and default handler is None\n"
+            )
             self.emittedNoHandlerWarning = True
             return
 
+        emitted = False
         if record.levelno >= self._level:
             for handler in self._handlers:
                 if record.levelno >= handler.level:
                     handler.emit(record)
+                    emitted = True
+
+            if (
+                not emitted
+                and _default_handler
+                and record.levelno >= _default_handler.level
+            ):
+                _default_handler.emit(record)
 
     def log(self, level: int, msg: str, *args) -> None:
         """Log a message.

examples/logging_simpletest.py

@@ -8,22 +8,31 @@
 
 import adafruit_logging as logging
 
-# This should produce an error output
+# This should produce an info output via default handler.
+
+logger_default_handler = logging.getLogger("default_handler")
+logger_default_handler.setLevel(logging.INFO)
+logger_default_handler.info("Default handler: Info message")
+assert not logger_default_handler.hasHandlers()
+
+# This should produce an error output via Stream Handler.
 
 logger = logging.getLogger("test")
-print_logger = logging.StreamHandler()
-logger.addHandler(print_logger)
+print_handler = logging.StreamHandler()
+logger.addHandler(print_handler)
+assert logger.hasHandlers()
 
 logger.setLevel(logging.ERROR)
-logger.info("Info message")
-logger.error("Error message")
+logger.info("Stream Handler: Info message")
+logger.error("Stream Handler: Error message")
 
-# This should produce no output
+# This should produce no output at all.
 
 null_logger = logging.getLogger("null")
 null_handler = logging.NullHandler()
 null_logger.addHandler(null_handler)
+assert null_logger.hasHandlers()
 
 null_logger.setLevel(logging.ERROR)
-null_logger.info("Info message")
-null_logger.error("Error message")
+null_logger.info("Null Handler: Info message")
+null_logger.error("Null Handler: Error message")