Fix logging_formatter keyerror breaking change (#42122)

Author: lzchen

sdk/monitor/azure-monitor-opentelemetry/CHANGELOG.md

@@ -8,6 +8,9 @@
 
 ### Bugs Fixed
 
+- Fix logging formatter breaking change
+    ([#42122](https://github.com/Azure/azure-sdk-for-python/pull/42122))
+
 ### Other Changes
 
 ## 1.6.11 (2025-07-17)

sdk/monitor/azure-monitor-opentelemetry/azure/monitor/opentelemetry/_configure.py

@@ -5,7 +5,7 @@
 # --------------------------------------------------------------------------
 from functools import cached_property
 from logging import getLogger, Formatter
-from typing import Dict, List, cast
+from typing import Dict, List, Optional, cast
 
 from opentelemetry.instrumentation.instrumentor import (  # type: ignore
     BaseInstrumentor,
@@ -194,7 +194,7 @@ def _setup_logging(configurations: Dict[str, ConfigurationValue]):
         logger_provider.add_log_record_processor(log_record_processor)
         set_logger_provider(logger_provider)
         logger_name: str = configurations[LOGGER_NAME_ARG]  # type: ignore
-        logging_formatter: Formatter = configurations[LOGGING_FORMATTER_ARG]  # type: ignore
+        logging_formatter: Optional[Formatter] = configurations.get(LOGGING_FORMATTER_ARG)  # type: ignore
         logger = getLogger(logger_name)
         # Only add OpenTelemetry LoggingHandler if logger does not already have the handler
         # This is to prevent most duplicate logging telemetry

sdk/monitor/azure-monitor-opentelemetry/tests/utils/test_configurations.py

@@ -330,7 +330,7 @@ def test_get_configurations_logging_format_env_var_invalid_format(self, mock_log
         configurations = _get_configurations()
 
         # Should be None when format is invalid
-        self.assertIsNone(configurations["logging_formatter"])
+        self.assertIsNone(configurations.get("logging_formatter"))
         # Should log a warning
         mock_logger.warning.assert_called_once()
         call_args = mock_logger.warning.call_args[0]