Fix mypy linting issues for Python 3.9 compatibility

- Reorder convert_to_oci_tool checks to avoid unreachable code warning
- Fix type annotation in test_stream_vllm to use BaseMessageChunk

Author: fede-kamel

libs/oci/langchain_oci/chat_models/oci_generative_ai.py

@@ -945,22 +945,8 @@ def convert_to_oci_tool(
         Raises:
             ValueError: If the tool type is not supported.
         """
-        if (isinstance(tool, type) and issubclass(tool, BaseModel)) or callable(tool):
-            as_json_schema_function = convert_to_openai_function(tool)
-            parameters = as_json_schema_function.get("parameters", {})
-            return self.oci_function_definition(
-                name=as_json_schema_function.get("name"),
-                description=as_json_schema_function.get(
-                    "description",
-                    as_json_schema_function.get("name"),
-                ),
-                parameters={
-                    "type": "object",
-                    "properties": parameters.get("properties", {}),
-                    "required": parameters.get("required", []),
-                },
-            )
-        elif isinstance(tool, BaseTool):
+        # Check BaseTool first since it's callable but needs special handling
+        if isinstance(tool, BaseTool):
             return self.oci_function_definition(
                 name=tool.name,
                 description=OCIUtils.remove_signature_from_tool_description(
@@ -982,6 +968,21 @@ def convert_to_oci_tool(
                     ],
                 },
             )
+        if (isinstance(tool, type) and issubclass(tool, BaseModel)) or callable(tool):
+            as_json_schema_function = convert_to_openai_function(tool)
+            parameters = as_json_schema_function.get("parameters", {})
+            return self.oci_function_definition(
+                name=as_json_schema_function.get("name"),
+                description=as_json_schema_function.get(
+                    "description",
+                    as_json_schema_function.get("name"),
+                ),
+                parameters={
+                    "type": "object",
+                    "properties": parameters.get("properties", {}),
+                    "required": parameters.get("required", []),
+                },
+            )
         raise ValueError(
             f"Unsupported tool type {type(tool)}. "
             "Tool must be passed in as a BaseTool "

libs/oci/tests/unit_tests/chat_models/test_oci_data_science.py

@@ -5,7 +5,7 @@
 from unittest import mock
 
 import pytest
-from langchain_core.messages import AIMessage, AIMessageChunk
+from langchain_core.messages import AIMessage, AIMessageChunk, BaseMessageChunk
 from requests.exceptions import HTTPError
 
 from langchain_oci.chat_models import (
@@ -145,7 +145,7 @@ def test_stream_vllm(*args: Any) -> None:
         endpoint=CONST_ENDPOINT, model=CONST_MODEL_NAME, streaming=True
     )
     assert llm._headers().get("route") == CONST_COMPLETION_ROUTE
-    output: Optional[AIMessageChunk] = None
+    output: Optional[BaseMessageChunk] = None
     count = 0
     for chunk in llm.stream(CONST_PROMPT):
         assert isinstance(chunk, AIMessageChunk)
@@ -156,8 +156,7 @@ def test_stream_vllm(*args: Any) -> None:
         count += 1
     assert count == 5
     assert output is not None
-    if output is not None:
-        assert str(output.content).strip() == CONST_COMPLETION
+    assert str(output.content).strip() == CONST_COMPLETION
 
 
 async def mocked_async_streaming_response(