wrap_model_call() — langchain Function Reference

Architecture documentation for the wrap_model_call() function in types.py from the langchain codebase.

Function python LangChainCore LanguageModelBase calls 1 called by 1

Entity Profile

LangChainCore→ LanguageModelBase→ wrap_model_call() — langchain Function Reference

Dependency Diagram

graph TD
  4c44eeee_7275_fead_c30b_9fbc9dff5261["wrap_model_call()"]
  949c7cf4_56fe_f3b4_cd89_9631a7e9cb1e["AgentMiddleware"]
  4c44eeee_7275_fead_c30b_9fbc9dff5261 -->|defined in| 949c7cf4_56fe_f3b4_cd89_9631a7e9cb1e
  500f1e07_60be_163a_141c_779d2c09ffd2["wrap_model_call()"]
  500f1e07_60be_163a_141c_779d2c09ffd2 -->|calls| 4c44eeee_7275_fead_c30b_9fbc9dff5261
  500f1e07_60be_163a_141c_779d2c09ffd2["wrap_model_call()"]
  4c44eeee_7275_fead_c30b_9fbc9dff5261 -->|calls| 500f1e07_60be_163a_141c_779d2c09ffd2
  style 4c44eeee_7275_fead_c30b_9fbc9dff5261 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/langchain_v1/langchain/agents/middleware/types.py lines 478–571

    def wrap_model_call(
        self,
        request: ModelRequest[ContextT],
        handler: Callable[[ModelRequest[ContextT]], ModelResponse[ResponseT]],
    ) -> ModelResponse[ResponseT] | AIMessage | ExtendedModelResponse[ResponseT]:
        """Intercept and control model execution via handler callback.

        Async version is `awrap_model_call`

        The handler callback executes the model request and returns a `ModelResponse`.
        Middleware can call the handler multiple times for retry logic, skip calling
        it to short-circuit, or modify the request/response. Multiple middleware
        compose with first in list as outermost layer.

        Args:
            request: Model request to execute (includes state and runtime).
            handler: Callback that executes the model request and returns
                `ModelResponse`.

                Call this to execute the model.

                Can be called multiple times for retry logic.

                Can skip calling it to short-circuit.

        Returns:
            The model call result.

        Examples:
            !!! example "Retry on error"

                ```python
                def wrap_model_call(self, request, handler):
                    for attempt in range(3):
                        try:
                            return handler(request)
                        except Exception:
                            if attempt == 2:
                                raise
                ```

            !!! example "Rewrite response"

                ```python
                def wrap_model_call(self, request, handler):
                    response = handler(request)
                    ai_msg = response.result[0]
                    return ModelResponse(
                        result=[AIMessage(content=f"[{ai_msg.content}]")],
                        structured_response=response.structured_response,
                    )
                ```

            !!! example "Error to fallback"

                ```python
                def wrap_model_call(self, request, handler):
                    try:
                        return handler(request)
                    except Exception:
                        return ModelResponse(result=[AIMessage(content="Service unavailable")])
                ```

            !!! example "Cache/short-circuit"

                ```python
                def wrap_model_call(self, request, handler):
                    if cached := get_cache(request):
                        return cached  # Short-circuit with cached result
                    response = handler(request)
                    save_cache(request, response)
                    return response
                ```

            !!! example "Simple `AIMessage` return (converted automatically)"

                ```python
                def wrap_model_call(self, request, handler):
                    response = handler(request)
                    # Can return AIMessage directly for simple cases
                    return AIMessage(content="Simplified response")