Add changelog and unit test for slash-delimited handler fix

- Add changelog entry in Unreleased section
- Add unit test verifying both slash and dot-delimited handler paths work
- Test confirms instrumentation handles both formats correctly

Related to #1465

Author: DivMode

CHANGELOG.md

@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- `opentelemetry-instrumentation-aws-lambda`: Fix ImportError with slash-delimited handler paths
+  ([#1465](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/1465))
+
 ## Version 1.38.0/0.59b0 (2025-10-16)
 
 ### Fixed

instrumentation/opentelemetry-instrumentation-aws-lambda/tests/test_aws_lambda_instrumentation_manual.py

@@ -727,6 +727,53 @@ def test_sqs_event_sets_attributes(self):
             MOCK_LAMBDA_CONTEXT_ATTRIBUTES,
         )
 
+    def test_slash_delimited_handler_path(self):
+        """Test that slash-delimited handler paths work correctly.
+
+        AWS Lambda accepts both slash-delimited (python/functions/api.handler)
+        and dot-delimited (python.functions.api.handler) handler paths.
+        This test ensures the instrumentation handles both formats.
+        """
+        # Test slash-delimited format
+        slash_env_patch = mock.patch.dict(
+            "os.environ",
+            {_HANDLER: "tests/mocks/lambda_function.handler"},
+        )
+        slash_env_patch.start()
+        AwsLambdaInstrumentor().instrument()
+
+        mock_execute_lambda()
+
+        spans = self.memory_exporter.get_finished_spans()
+        self.assertEqual(len(spans), 1)
+        self.assertSpanHasAttributes(
+            spans[0],
+            MOCK_LAMBDA_CONTEXT_ATTRIBUTES,
+        )
+
+        slash_env_patch.stop()
+        AwsLambdaInstrumentor().uninstrument()
+        self.memory_exporter.clear()
+
+        # Test dot-delimited format (should still work)
+        dot_env_patch = mock.patch.dict(
+            "os.environ",
+            {_HANDLER: "tests.mocks.lambda_function.handler"},
+        )
+        dot_env_patch.start()
+        AwsLambdaInstrumentor().instrument()
+
+        mock_execute_lambda()
+
+        spans = self.memory_exporter.get_finished_spans()
+        self.assertEqual(len(spans), 1)
+        self.assertSpanHasAttributes(
+            spans[0],
+            MOCK_LAMBDA_CONTEXT_ATTRIBUTES,
+        )
+
+        dot_env_patch.stop()
+
     def test_lambda_handles_handler_exception_with_api_gateway_proxy_event(
         self,
     ):