expose function for converting messages to messages (#8426)

libs/langchain/langchain/chat_models/openai.py

@@ -142,6 +142,18 @@ def _convert_dict_to_message(_dict: Mapping[str, Any]) -> BaseMessage:
         return ChatMessage(content=_dict["content"], role=role)
 
 
+def convert_openai_messages(messages: List[dict]) -> List[BaseMessage]:
+    """Convert dictionaries representing OpenAI messages to LangChain format.
+
+    Args:
+        messages: List of dictionaries representing OpenAI messages
+
+    Returns:
+        List of LangChain BaseMessage objects.
+    """
+    return [_convert_dict_to_message(m) for m in messages]
+
+
 def _convert_message_to_dict(message: BaseMessage) -> dict:
     if isinstance(message, ChatMessage):
         message_dict = {"role": message.role, "content": message.content}

libs/langchain/tests/unit_tests/chat_models/test_openai.py

@@ -9,7 +9,12 @@ from langchain.chat_models.openai import (
     ChatOpenAI,
     _convert_dict_to_message,
 )
-from langchain.schema.messages import FunctionMessage
+from langchain.schema.messages import (
+    AIMessage,
+    FunctionMessage,
+    HumanMessage,
+    SystemMessage,
+)
 
 
 def test_function_message_dict_to_function_message() -> None:
@@ -27,6 +32,27 @@ def test_function_message_dict_to_function_message() -> None:
     assert result.content == content
 
 
+def test__convert_dict_to_message_human() -> None:
+    message = {"role": "user", "content": "foo"}
+    result = _convert_dict_to_message(message)
+    expected_output = HumanMessage(content="foo")
+    assert result == expected_output
+
+
+def test__convert_dict_to_message_ai() -> None:
+    message = {"role": "assistant", "content": "foo"}
+    result = _convert_dict_to_message(message)
+    expected_output = AIMessage(content="foo")
+    assert result == expected_output
+
+
+def test__convert_dict_to_message_system() -> None:
+    message = {"role": "system", "content": "foo"}
+    result = _convert_dict_to_message(message)
+    expected_output = SystemMessage(content="foo")
+    assert result == expected_output
+
+
 @pytest.fixture
 def mock_completion() -> dict:
     return {