mistralai: support method="json_schema" in structured output (#29461)

https://docs.mistral.ai/capabilities/structured-output/custom_structured_output/

libs/partners/mistralai/langchain_mistralai/chat_models.py

@@ -686,7 +686,9 @@ class ChatMistralAI(BaseChatModel):
         self,
         schema: Optional[Union[Dict, Type]] = None,
         *,
-        method: Literal["function_calling", "json_mode"] = "function_calling",
+        method: Literal[
+            "function_calling", "json_mode", "json_schema"
+        ] = "function_calling",
         include_raw: bool = False,
         **kwargs: Any,
     ) -> Runnable[LanguageModelInput, Union[Dict, BaseModel]]:
@@ -710,13 +712,25 @@ class ChatMistralAI(BaseChatModel):
 
                         Added support for TypedDict class.
 
-            method:
+            method: The method for steering model generation, one of:
-                The method for steering model generation, either "function_calling"
+
-                or "json_mode". If "function_calling" then the schema will be converted
+                - "function_calling":
-                to an OpenAI function and the returned model will make use of the
+                    Uses Mistral's
-                function-calling API. If "json_mode" then OpenAI's JSON mode will be
+                    `function-calling feature <https://docs.mistral.ai/capabilities/function_calling/>`_.
-                used. Note that if using "json_mode" then you must include instructions
+                - "json_schema":
-                for formatting the output into the desired schema into the model call.
+                    Uses Mistral's
+                    `structured output feature <https://docs.mistral.ai/capabilities/structured-output/custom_structured_output/>`_.
+                - "json_mode":
+                    Uses Mistral's
+                    `JSON mode <https://docs.mistral.ai/capabilities/structured-output/json_mode/>`_.
+                    Note that if using JSON mode then you
+                    must include instructions for formatting the output into the
+                    desired schema into the model call.
+
+                .. versionchanged:: 0.2.5
+
+                        Added method="json_schema"
+
             include_raw:
                 If False then only the parsed structured output is returned. If
                 an error occurs during model output parsing it will be raised. If True
@@ -877,11 +891,11 @@ class ChatMistralAI(BaseChatModel):
 
                 structured_llm.invoke(
                     "Answer the following question. "
-                    "Make sure to return a JSON blob with keys 'answer' and 'justification'.\n\n"
+                    "Make sure to return a JSON blob with keys 'answer' and 'justification'.\\n\\n"
                     "What's heavier a pound of bricks or a pound of feathers?"
                 )
                 # -> {
-                #     'raw': AIMessage(content='{\n    "answer": "They are both the same weight.",\n    "justification": "Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight." \n}'),
+                #     'raw': AIMessage(content='{\\n    "answer": "They are both the same weight.",\\n    "justification": "Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight." \\n}'),
                 #     'parsed': AnswerWithJustification(answer='They are both the same weight.', justification='Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight.'),
                 #     'parsing_error': None
                 # }
@@ -893,17 +907,18 @@ class ChatMistralAI(BaseChatModel):
 
                 structured_llm.invoke(
                     "Answer the following question. "
-                    "Make sure to return a JSON blob with keys 'answer' and 'justification'.\n\n"
+                    "Make sure to return a JSON blob with keys 'answer' and 'justification'.\\n\\n"
                     "What's heavier a pound of bricks or a pound of feathers?"
                 )
                 # -> {
-                #     'raw': AIMessage(content='{\n    "answer": "They are both the same weight.",\n    "justification": "Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight." \n}'),
+                #     'raw': AIMessage(content='{\\n    "answer": "They are both the same weight.",\\n    "justification": "Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight." \\n}'),
                 #     'parsed': {
                 #         'answer': 'They are both the same weight.',
                 #         'justification': 'Both a pound of bricks and a pound of feathers weigh one pound. The difference lies in the volume and density of the materials, not the weight.'
                 #     },
                 #     'parsing_error': None
                 # }
+
         """  # noqa: E501
         if kwargs:
             raise ValueError(f"Received unsupported arguments {kwargs}")
@@ -934,6 +949,20 @@ class ChatMistralAI(BaseChatModel):
                 if is_pydantic_schema
                 else JsonOutputParser()
             )
+        elif method == "json_schema":
+            if schema is None:
+                raise ValueError(
+                    "schema must be specified when method is 'json_schema'. "
+                    "Received None."
+                )
+            response_format = _convert_to_openai_response_format(schema, strict=True)
+            llm = self.bind(response_format=response_format)
+
+            output_parser = (
+                PydanticOutputParser(pydantic_object=schema)  # type: ignore[arg-type]
+                if is_pydantic_schema
+                else JsonOutputParser()
+            )
         if include_raw:
             parser_assign = RunnablePassthrough.assign(
                 parsed=itemgetter("raw") | output_parser, parsing_error=lambda _: None
@@ -969,3 +998,38 @@ class ChatMistralAI(BaseChatModel):
     def get_lc_namespace(cls) -> List[str]:
         """Get the namespace of the langchain object."""
         return ["langchain", "chat_models", "mistralai"]
+
+
+def _convert_to_openai_response_format(
+    schema: Union[Dict[str, Any], Type], *, strict: Optional[bool] = None
+) -> Dict:
+    """Same as in ChatOpenAI, but don't pass through Pydantic BaseModels."""
+    if (
+        isinstance(schema, dict)
+        and "json_schema" in schema
+        and schema.get("type") == "json_schema"
+    ):
+        response_format = schema
+    elif isinstance(schema, dict) and "name" in schema and "schema" in schema:
+        response_format = {"type": "json_schema", "json_schema": schema}
+    else:
+        if strict is None:
+            if isinstance(schema, dict) and isinstance(schema.get("strict"), bool):
+                strict = schema["strict"]
+            else:
+                strict = False
+        function = convert_to_openai_tool(schema, strict=strict)["function"]
+        function["schema"] = function.pop("parameters")
+        response_format = {"type": "json_schema", "json_schema": function}
+
+    if strict is not None and strict is not response_format["json_schema"].get(
+        "strict"
+    ):
+        msg = (
+            f"Output schema already has 'strict' value set to "
+            f"{schema['json_schema']['strict']} but 'strict' also passed in to "
+            f"with_structured_output as {strict}. Please make sure that "
+            f"'strict' is only specified in one place."
+        )
+        raise ValueError(msg)
+    return response_format

libs/partners/mistralai/tests/integration_tests/test_chat_models.py

@@ -3,6 +3,7 @@
 import json
 from typing import Any, Optional
 
+import pytest
 from langchain_core.messages import (
     AIMessage,
     AIMessageChunk,
@@ -10,6 +11,7 @@ from langchain_core.messages import (
     HumanMessage,
 )
 from pydantic import BaseModel
+from typing_extensions import TypedDict
 
 from langchain_mistralai.chat_models import ChatMistralAI
 
@@ -176,6 +178,65 @@ def test_streaming_structured_output() -> None:
         chunk_num += 1
 
 
+class Book(BaseModel):
+    name: str
+    authors: list[str]
+
+
+class BookDict(TypedDict):
+    name: str
+    authors: list[str]
+
+
+def _check_parsed_result(result: Any, schema: Any) -> None:
+    if schema == Book:
+        assert isinstance(result, Book)
+    elif schema == BookDict:
+        assert all(key in ["name", "authors"] for key in result.keys())
+
+
+@pytest.mark.parametrize("schema", [Book, BookDict, Book.model_json_schema()])
+def test_structured_output_json_schema(schema: Any) -> None:
+    llm = ChatMistralAI(model="ministral-8b-latest")  # type: ignore[call-arg]
+    structured_llm = llm.with_structured_output(schema, method="json_schema")
+
+    messages = [
+        {"role": "system", "content": "Extract the book's information."},
+        {
+            "role": "user",
+            "content": "I recently read 'To Kill a Mockingbird' by Harper Lee.",
+        },
+    ]
+    # Test invoke
+    result = structured_llm.invoke(messages)
+    _check_parsed_result(result, schema)
+
+    # Test stream
+    for chunk in structured_llm.stream(messages):
+        _check_parsed_result(chunk, schema)
+
+
+@pytest.mark.parametrize("schema", [Book, BookDict, Book.model_json_schema()])
+async def test_structured_output_json_schema_async(schema: Any) -> None:
+    llm = ChatMistralAI(model="ministral-8b-latest")  # type: ignore[call-arg]
+    structured_llm = llm.with_structured_output(schema, method="json_schema")
+
+    messages = [
+        {"role": "system", "content": "Extract the book's information."},
+        {
+            "role": "user",
+            "content": "I recently read 'To Kill a Mockingbird' by Harper Lee.",
+        },
+    ]
+    # Test invoke
+    result = await structured_llm.ainvoke(messages)
+    _check_parsed_result(result, schema)
+
+    # Test stream
+    async for chunk in structured_llm.astream(messages):
+        _check_parsed_result(chunk, schema)
+
+
 def test_tool_call() -> None:
     llm = ChatMistralAI(model="mistral-large-latest", temperature=0)  # type: ignore[call-arg]