Handle "LogRecord.exc_info" being a string

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Fix logic to deal with `LoggingHandler.exc_info` occasionally being a string ([#4699](https://github.com/open-telemetry/opentelemetry-python/pull/4699))
+
 ## Version 1.36.0/0.57b0 (2025-07-29)
 
 - Add missing Prometheus exporter documentation

opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py

@@ -19,6 +19,7 @@
 import concurrent.futures
 import json
 import logging
+import sys
 import threading
 import traceback
 import warnings
@@ -568,6 +569,9 @@ def _get_attributes(record: logging.LogRecord) -> _ExtendedAttributes:
         attributes[code_attributes.CODE_FUNCTION_NAME] = record.funcName
         attributes[code_attributes.CODE_LINE_NUMBER] = record.lineno
 
+        if isinstance(record.exc_info, str):
+            record.exc_info = sys.exc_info()
+
         if record.exc_info:
             exctype, value, tb = record.exc_info
             if exctype is not None:

opentelemetry-sdk/tests/logs/test_handler.py

@@ -14,6 +14,8 @@
 
 import logging
 import os
+import sys
+import traceback
 import unittest
 from unittest.mock import Mock, patch
 
@@ -48,6 +50,39 @@ def test_handler_default_log_level(self):
             logger.warning("Warning message")
         self.assertEqual(processor.emit_count(), 1)
 
+    def test_handler_error_exc_info(self):
+        processor, logger = set_up_test_logging(logging.NOTSET)
+
+        class CustomException(Exception):
+            pass
+
+        try:
+            raise CustomException("Custom exception")
+        except CustomException as exception:
+            exc_info = (type(exception), exception, exception.__traceback__)
+        else:
+            exc_info = "Second stringified exception"
+
+        exc_info_values = [
+            # Don't know what caused it in my context, so I'm relying on mocks to replicate the behavior.
+            # First the `record.exc_info` becomes a string somehow, then `sys.exc_info` brings the tuple.
+            "First stringified exception",
+            exc_info,
+        ]
+
+        with patch.object(sys, "exc_info", side_effect=exc_info_values):
+            logger.exception("Exception message")  # Should not raise exception
+
+        assert processor.emit_count() == 1
+
+        attributes = processor.log_data_emitted[0].log_record.attributes._dict
+        assert attributes["exception.type"] == "CustomException"
+        assert attributes["exception.message"] == str(exc_info[1])
+        assert isinstance(exc_info, tuple)
+        assert attributes["exception.stacktrace"] == "".join(
+            traceback.format_exception(*exc_info)
+        )
+
     def test_handler_custom_log_level(self):
         processor, logger = set_up_test_logging(logging.ERROR)