React

ReActAgent

Bases: AgentRunner

ReAct agent.

Subclasses AgentRunner with a ReActAgentWorker.

For the legacy implementation see:

from llama_index.core.agent.legacy.react.base import ReActAgent

Source code in llama-index-core/llama_index/core/agent/react/base.py

class ReActAgent(AgentRunner):
    """ReAct agent.

    Subclasses AgentRunner with a ReActAgentWorker.

    For the legacy implementation see:
    ```python
    from llama_index.core.agent.legacy.react.base import ReActAgent
    ```

    """

    def __init__(
        self,
        tools: Sequence[BaseTool],
        llm: LLM,
        memory: BaseMemory,
        max_iterations: int = 10,
        react_chat_formatter: Optional[ReActChatFormatter] = None,
        output_parser: Optional[ReActOutputParser] = None,
        callback_manager: Optional[CallbackManager] = None,
        verbose: bool = False,
        tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
        context: Optional[str] = None,
        handle_reasoning_failure_fn: Optional[
            Callable[[CallbackManager, Exception], ToolOutput]
        ] = None,
    ) -> None:
        """Init params."""
        callback_manager = callback_manager or llm.callback_manager
        if context and react_chat_formatter:
            raise ValueError("Cannot provide both context and react_chat_formatter")
        if context:
            react_chat_formatter = ReActChatFormatter.from_context(context)

        step_engine = ReActAgentWorker.from_tools(
            tools=tools,
            tool_retriever=tool_retriever,
            llm=llm,
            max_iterations=max_iterations,
            react_chat_formatter=react_chat_formatter,
            output_parser=output_parser,
            callback_manager=callback_manager,
            verbose=verbose,
            handle_reasoning_failure_fn=handle_reasoning_failure_fn,
        )
        super().__init__(
            step_engine,
            memory=memory,
            llm=llm,
            callback_manager=callback_manager,
        )

    @classmethod
    def from_tools(
        cls,
        tools: Optional[List[BaseTool]] = None,
        tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
        llm: Optional[LLM] = None,
        chat_history: Optional[List[ChatMessage]] = None,
        memory: Optional[BaseMemory] = None,
        memory_cls: Type[BaseMemory] = ChatMemoryBuffer,
        max_iterations: int = 10,
        react_chat_formatter: Optional[ReActChatFormatter] = None,
        output_parser: Optional[ReActOutputParser] = None,
        callback_manager: Optional[CallbackManager] = None,
        verbose: bool = False,
        context: Optional[str] = None,
        handle_reasoning_failure_fn: Optional[
            Callable[[CallbackManager, Exception], ToolOutput]
        ] = None,
        **kwargs: Any,
    ) -> "ReActAgent":
        """Convenience constructor method from set of BaseTools (Optional).

        NOTE: kwargs should have been exhausted by this point. In other words
        the various upstream components such as BaseSynthesizer (response synthesizer)
        or BaseRetriever should have picked up off their respective kwargs in their
        constructions.

        If `handle_reasoning_failure_fn` is provided, when LLM fails to follow the response templates specified in
        the System Prompt, this function will be called. This function should provide to the Agent, so that the Agent
        can have a second chance to fix its mistakes.
        To handle the exception yourself, you can provide a function that raises the `Exception`.

        Note: If you modified any response template in the System Prompt, you should override the method
        `_extract_reasoning_step` in `ReActAgentWorker`.

        Returns:
            ReActAgent
        """
        llm = llm or Settings.llm
        if callback_manager is not None:
            llm.callback_manager = callback_manager
        memory = memory or memory_cls.from_defaults(
            chat_history=chat_history or [], llm=llm
        )
        return cls(
            tools=tools or [],
            tool_retriever=tool_retriever,
            llm=llm,
            memory=memory,
            max_iterations=max_iterations,
            react_chat_formatter=react_chat_formatter,
            output_parser=output_parser,
            callback_manager=callback_manager,
            verbose=verbose,
            context=context,
            handle_reasoning_failure_fn=handle_reasoning_failure_fn,
        )

    def _get_prompt_modules(self) -> PromptMixinType:
        """Get prompt modules."""
        return {"agent_worker": self.agent_worker}

from_tools classmethod

from_tools(tools: Optional[List[BaseTool]] = None, tool_retriever: Optional[ObjectRetriever[BaseTool]] = None, llm: Optional[LLM] = None, chat_history: Optional[List[ChatMessage]] = None, memory: Optional[BaseMemory] = None, memory_cls: Type[BaseMemory] = ChatMemoryBuffer, max_iterations: int = 10, react_chat_formatter: Optional[ReActChatFormatter] = None, output_parser: Optional[ReActOutputParser] = None, callback_manager: Optional[CallbackManager] = None, verbose: bool = False, context: Optional[str] = None, handle_reasoning_failure_fn: Optional[Callable[[CallbackManager, Exception], ToolOutput]] = None, **kwargs: Any) -> ReActAgent

Convenience constructor method from set of BaseTools (Optional).

NOTE: kwargs should have been exhausted by this point. In other words the various upstream components such as BaseSynthesizer (response synthesizer) or BaseRetriever should have picked up off their respective kwargs in their constructions.

If handle_reasoning_failure_fn is provided, when LLM fails to follow the response templates specified in the System Prompt, this function will be called. This function should provide to the Agent, so that the Agent can have a second chance to fix its mistakes. To handle the exception yourself, you can provide a function that raises the Exception.

Note: If you modified any response template in the System Prompt, you should override the method _extract_reasoning_step in ReActAgentWorker.

Returns:

Type	Description
ReActAgent	ReActAgent

Source code in llama-index-core/llama_index/core/agent/react/base.py

@classmethod
def from_tools(
    cls,
    tools: Optional[List[BaseTool]] = None,
    tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
    llm: Optional[LLM] = None,
    chat_history: Optional[List[ChatMessage]] = None,
    memory: Optional[BaseMemory] = None,
    memory_cls: Type[BaseMemory] = ChatMemoryBuffer,
    max_iterations: int = 10,
    react_chat_formatter: Optional[ReActChatFormatter] = None,
    output_parser: Optional[ReActOutputParser] = None,
    callback_manager: Optional[CallbackManager] = None,
    verbose: bool = False,
    context: Optional[str] = None,
    handle_reasoning_failure_fn: Optional[
        Callable[[CallbackManager, Exception], ToolOutput]
    ] = None,
    **kwargs: Any,
) -> "ReActAgent":
    """Convenience constructor method from set of BaseTools (Optional).

    NOTE: kwargs should have been exhausted by this point. In other words
    the various upstream components such as BaseSynthesizer (response synthesizer)
    or BaseRetriever should have picked up off their respective kwargs in their
    constructions.

    If `handle_reasoning_failure_fn` is provided, when LLM fails to follow the response templates specified in
    the System Prompt, this function will be called. This function should provide to the Agent, so that the Agent
    can have a second chance to fix its mistakes.
    To handle the exception yourself, you can provide a function that raises the `Exception`.

    Note: If you modified any response template in the System Prompt, you should override the method
    `_extract_reasoning_step` in `ReActAgentWorker`.

    Returns:
        ReActAgent
    """
    llm = llm or Settings.llm
    if callback_manager is not None:
        llm.callback_manager = callback_manager
    memory = memory or memory_cls.from_defaults(
        chat_history=chat_history or [], llm=llm
    )
    return cls(
        tools=tools or [],
        tool_retriever=tool_retriever,
        llm=llm,
        memory=memory,
        max_iterations=max_iterations,
        react_chat_formatter=react_chat_formatter,
        output_parser=output_parser,
        callback_manager=callback_manager,
        verbose=verbose,
        context=context,
        handle_reasoning_failure_fn=handle_reasoning_failure_fn,
    )

ReActAgentWorker

Bases: BaseAgentWorker

OpenAI Agent worker.

Source code in llama-index-core/llama_index/core/agent/react/step.py

class ReActAgentWorker(BaseAgentWorker):
    """OpenAI Agent worker."""

    def __init__(
        self,
        tools: Sequence[BaseTool],
        llm: LLM,
        max_iterations: int = 10,
        react_chat_formatter: Optional[ReActChatFormatter] = None,
        output_parser: Optional[ReActOutputParser] = None,
        callback_manager: Optional[CallbackManager] = None,
        verbose: bool = False,
        tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
        handle_reasoning_failure_fn: Optional[
            Callable[[CallbackManager, Exception], ToolOutput]
        ] = None,
    ) -> None:
        self._llm = llm
        self.callback_manager = callback_manager or llm.callback_manager
        self._max_iterations = max_iterations
        self._react_chat_formatter = react_chat_formatter or ReActChatFormatter()
        self._output_parser = output_parser or ReActOutputParser()
        self._verbose = verbose
        self._handle_reasoning_failure_fn = (
            handle_reasoning_failure_fn
            or tell_llm_about_failure_in_extract_reasoning_step
        )

        if len(tools) > 0 and tool_retriever is not None:
            raise ValueError("Cannot specify both tools and tool_retriever")
        elif len(tools) > 0:
            self._get_tools = lambda _: tools
        elif tool_retriever is not None:
            tool_retriever_c = cast(ObjectRetriever[BaseTool], tool_retriever)
            self._get_tools = lambda message: tool_retriever_c.retrieve(message)
        else:
            self._get_tools = lambda _: []

    @classmethod
    def from_tools(
        cls,
        tools: Optional[Sequence[BaseTool]] = None,
        tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
        llm: Optional[LLM] = None,
        max_iterations: int = 10,
        react_chat_formatter: Optional[ReActChatFormatter] = None,
        output_parser: Optional[ReActOutputParser] = None,
        callback_manager: Optional[CallbackManager] = None,
        verbose: bool = False,
        handle_reasoning_failure_fn: Optional[
            Callable[[CallbackManager, Exception], ToolOutput]
        ] = None,
        **kwargs: Any,
    ) -> "ReActAgentWorker":
        """Convenience constructor method from set of BaseTools (Optional).

        NOTE: kwargs should have been exhausted by this point. In other words
        the various upstream components such as BaseSynthesizer (response synthesizer)
        or BaseRetriever should have picked up off their respective kwargs in their
        constructions.

        Returns:
            ReActAgentWorker
        """
        llm = llm or Settings.llm
        if callback_manager is not None:
            llm.callback_manager = callback_manager
        return cls(
            tools=tools or [],
            tool_retriever=tool_retriever,
            llm=llm,
            max_iterations=max_iterations,
            react_chat_formatter=react_chat_formatter,
            output_parser=output_parser,
            callback_manager=callback_manager,
            verbose=verbose,
            handle_reasoning_failure_fn=handle_reasoning_failure_fn,
        )

    def _get_prompts(self) -> PromptDictType:
        """Get prompts."""
        # TODO: the ReAct formatter does not explicitly specify PromptTemplate
        # objects, but wrap it in this to obey the interface
        sys_header = self._react_chat_formatter.system_header
        return {"system_prompt": PromptTemplate(sys_header)}

    def _update_prompts(self, prompts: PromptDictType) -> None:
        """Update prompts."""
        if "system_prompt" in prompts:
            sys_prompt = cast(PromptTemplate, prompts["system_prompt"])
            self._react_chat_formatter.system_header = sys_prompt.template

    def initialize_step(self, task: Task, **kwargs: Any) -> TaskStep:
        """Initialize step from task."""
        sources: List[ToolOutput] = []
        current_reasoning: List[BaseReasoningStep] = []
        # temporary memory for new messages
        new_memory = ChatMemoryBuffer.from_defaults()

        # initialize task state
        task_state = {
            "sources": sources,
            "current_reasoning": current_reasoning,
            "new_memory": new_memory,
        }
        task.extra_state.update(task_state)

        return TaskStep(
            task_id=task.task_id,
            step_id=str(uuid.uuid4()),
            input=task.input,
            step_state={"is_first": True},
        )

    def get_tools(self, input: str) -> List[AsyncBaseTool]:
        """Get tools."""
        return [adapt_to_async_tool(t) for t in self._get_tools(input)]

    def _extract_reasoning_step(
        self, output: ChatResponse, is_streaming: bool = False
    ) -> Tuple[str, List[BaseReasoningStep], bool]:
        """
        Extracts the reasoning step from the given output.

        This method parses the message content from the output,
        extracts the reasoning step, and determines whether the processing is
        complete. It also performs validation checks on the output and
        handles possible errors.
        """
        if output.message.content is None:
            raise ValueError("Got empty message.")
        message_content = output.message.content
        current_reasoning = []
        try:
            reasoning_step = self._output_parser.parse(message_content, is_streaming)
        except BaseException as exc:
            raise ValueError(f"Could not parse output: {message_content}") from exc
        if self._verbose:
            print_text(f"{reasoning_step.get_content()}\n", color="pink")
        current_reasoning.append(reasoning_step)

        if reasoning_step.is_done:
            return message_content, current_reasoning, True

        reasoning_step = cast(ActionReasoningStep, reasoning_step)
        if not isinstance(reasoning_step, ActionReasoningStep):
            raise ValueError(f"Expected ActionReasoningStep, got {reasoning_step}")

        return message_content, current_reasoning, False

    def _process_actions(
        self,
        task: Task,
        tools: Sequence[AsyncBaseTool],
        output: ChatResponse,
        is_streaming: bool = False,
    ) -> Tuple[List[BaseReasoningStep], bool]:
        tools_dict: Dict[str, AsyncBaseTool] = {
            tool.metadata.get_name(): tool for tool in tools
        }
        tool = None

        try:
            _, current_reasoning, is_done = self._extract_reasoning_step(
                output, is_streaming
            )
        except ValueError as exp:
            current_reasoning = []
            tool_output = self._handle_reasoning_failure_fn(self.callback_manager, exp)
        else:
            if is_done:
                return current_reasoning, True

            # call tool with input
            reasoning_step = cast(ActionReasoningStep, current_reasoning[-1])
            if reasoning_step.action in tools_dict:
                tool = tools_dict[reasoning_step.action]
                with self.callback_manager.event(
                    CBEventType.FUNCTION_CALL,
                    payload={
                        EventPayload.FUNCTION_CALL: reasoning_step.action_input,
                        EventPayload.TOOL: tool.metadata,
                    },
                ) as event:
                    try:
                        tool_output = tool.call(**reasoning_step.action_input)
                    except Exception as e:
                        tool_output = ToolOutput(
                            content=f"Error: {e!s}",
                            tool_name=tool.metadata.name,
                            raw_input={"kwargs": reasoning_step.action_input},
                            raw_output=e,
                            is_error=True,
                        )
                    event.on_end(
                        payload={EventPayload.FUNCTION_OUTPUT: str(tool_output)}
                    )
            else:
                tool_output = self._handle_nonexistent_tool_name(reasoning_step)

        task.extra_state["sources"].append(tool_output)

        observation_step = ObservationReasoningStep(
            observation=str(tool_output),
            return_direct=tool.metadata.return_direct and not tool_output.is_error
            if tool
            else False,
        )
        current_reasoning.append(observation_step)
        if self._verbose:
            print_text(f"{observation_step.get_content()}\n", color="blue")
        return (
            current_reasoning,
            tool.metadata.return_direct and not tool_output.is_error if tool else False,
        )

    async def _aprocess_actions(
        self,
        task: Task,
        tools: Sequence[AsyncBaseTool],
        output: ChatResponse,
        is_streaming: bool = False,
    ) -> Tuple[List[BaseReasoningStep], bool]:
        tools_dict = {tool.metadata.name: tool for tool in tools}
        tool = None

        try:
            _, current_reasoning, is_done = self._extract_reasoning_step(
                output, is_streaming
            )
        except ValueError as exp:
            current_reasoning = []
            tool_output = self._handle_reasoning_failure_fn(self.callback_manager, exp)
        else:
            if is_done:
                return current_reasoning, True

            # call tool with input
            reasoning_step = cast(ActionReasoningStep, current_reasoning[-1])
            if reasoning_step.action in tools_dict:
                tool = tools_dict[reasoning_step.action]
                with self.callback_manager.event(
                    CBEventType.FUNCTION_CALL,
                    payload={
                        EventPayload.FUNCTION_CALL: reasoning_step.action_input,
                        EventPayload.TOOL: tool.metadata,
                    },
                ) as event:
                    try:
                        tool_output = await tool.acall(**reasoning_step.action_input)
                    except Exception as e:
                        tool_output = ToolOutput(
                            content=f"Error: {e!s}",
                            tool_name=tool.metadata.name,
                            raw_input={"kwargs": reasoning_step.action_input},
                            raw_output=e,
                            is_error=True,
                        )
                    event.on_end(
                        payload={EventPayload.FUNCTION_OUTPUT: str(tool_output)}
                    )
            else:
                tool_output = self._handle_nonexistent_tool_name(reasoning_step)

        task.extra_state["sources"].append(tool_output)

        observation_step = ObservationReasoningStep(
            observation=str(tool_output),
            return_direct=tool.metadata.return_direct and not tool_output.is_error
            if tool
            else False,
        )
        current_reasoning.append(observation_step)
        if self._verbose:
            print_text(f"{observation_step.get_content()}\n", color="blue")
        return (
            current_reasoning,
            tool.metadata.return_direct and not tool_output.is_error if tool else False,
        )

    def _handle_nonexistent_tool_name(self, reasoning_step):
        # We still emit a `tool_output` object to the task, so that the LLM can know
        # it has hallucinated in the next reasoning step.
        with self.callback_manager.event(
            CBEventType.FUNCTION_CALL,
            payload={
                EventPayload.FUNCTION_CALL: reasoning_step.action_input,
            },
        ) as event:
            # TODO(L10N): This should be localized.
            content = f"Error: No such tool named `{reasoning_step.action}`."
            tool_output = ToolOutput(
                content=content,
                tool_name=reasoning_step.action,
                raw_input={"kwargs": reasoning_step.action_input},
                raw_output=content,
                is_error=True,
            )
            event.on_end(payload={EventPayload.FUNCTION_OUTPUT: str(tool_output)})
        return tool_output

    def _get_response(
        self,
        current_reasoning: List[BaseReasoningStep],
        sources: List[ToolOutput],
    ) -> AgentChatResponse:
        """Get response from reasoning steps."""
        if len(current_reasoning) == 0:
            raise ValueError("No reasoning steps were taken.")
        elif len(current_reasoning) == self._max_iterations:
            raise ValueError("Reached max iterations.")

        if isinstance(current_reasoning[-1], ResponseReasoningStep):
            response_step = cast(ResponseReasoningStep, current_reasoning[-1])
            response_str = response_step.response
        elif (
            isinstance(current_reasoning[-1], ObservationReasoningStep)
            and current_reasoning[-1].return_direct
        ):
            response_str = current_reasoning[-1].observation
        else:
            response_str = current_reasoning[-1].get_content()

        # TODO: add sources from reasoning steps
        return AgentChatResponse(response=response_str, sources=sources)

    def _get_task_step_response(
        self, agent_response: AGENT_CHAT_RESPONSE_TYPE, step: TaskStep, is_done: bool
    ) -> TaskStepOutput:
        """Get task step response."""
        if is_done:
            new_steps = []
        else:
            new_steps = [
                step.get_next_step(
                    step_id=str(uuid.uuid4()),
                    # NOTE: input is unused
                    input=None,
                )
            ]

        return TaskStepOutput(
            output=agent_response,
            task_step=step,
            is_last=is_done,
            next_steps=new_steps,
        )

    def _infer_stream_chunk_is_final(self, chunk: ChatResponse) -> bool:
        """Infers if a chunk from a live stream is the start of the final
        reasoning step. (i.e., and should eventually become
        ResponseReasoningStep — not part of this function's logic tho.).

        Args:
            chunk (ChatResponse): the current chunk stream to check

        Returns:
            bool: Boolean on whether the chunk is the start of the final response
        """
        latest_content = chunk.message.content
        if latest_content:
            # doesn't follow thought-action format
            if len(latest_content) > len("Thought") and not latest_content.startswith(
                "Thought"
            ):
                return True
            elif "Answer: " in latest_content:
                return True
        return False

    def _add_back_chunk_to_stream(
        self, chunk: ChatResponse, chat_stream: Generator[ChatResponse, None, None]
    ) -> Generator[ChatResponse, None, None]:
        """Helper method for adding back initial chunk stream of final response
        back to the rest of the chat_stream.

        Args:
            chunk (ChatResponse): the chunk to add back to the beginning of the
                                    chat_stream.

        Return:
            Generator[ChatResponse, None, None]: the updated chat_stream
        """
        updated_stream = chain.from_iterable(  # need to add back partial response chunk
            [
                unit_generator(chunk),
                chat_stream,
            ]
        )
        # use cast to avoid mypy issue with chain and Generator
        updated_stream_c: Generator[ChatResponse, None, None] = cast(
            Generator[ChatResponse, None, None], updated_stream
        )
        return updated_stream_c

    async def _async_add_back_chunk_to_stream(
        self, chunk: ChatResponse, chat_stream: AsyncGenerator[ChatResponse, None]
    ) -> AsyncGenerator[ChatResponse, None]:
        """Helper method for adding back initial chunk stream of final response
        back to the rest of the chat_stream.

        NOTE: this itself is not an async function.

        Args:
            chunk (ChatResponse): the chunk to add back to the beginning of the
                                    chat_stream.

        Return:
            AsyncGenerator[ChatResponse, None]: the updated async chat_stream
        """
        yield chunk
        async for item in chat_stream:
            yield item

    def _run_step(
        self,
        step: TaskStep,
        task: Task,
    ) -> TaskStepOutput:
        """Run step."""
        if step.input is not None:
            add_user_step_to_reasoning(
                step,
                task.extra_state["new_memory"],
                task.extra_state["current_reasoning"],
                verbose=self._verbose,
            )
        # TODO: see if we want to do step-based inputs
        tools = self.get_tools(task.input)
        input_chat = self._react_chat_formatter.format(
            tools,
            chat_history=task.memory.get() + task.extra_state["new_memory"].get_all(),
            current_reasoning=task.extra_state["current_reasoning"],
        )

        # send prompt
        chat_response = self._llm.chat(input_chat)
        # given react prompt outputs, call tools or return response
        reasoning_steps, is_done = self._process_actions(
            task, tools, output=chat_response
        )
        task.extra_state["current_reasoning"].extend(reasoning_steps)
        agent_response = self._get_response(
            task.extra_state["current_reasoning"], task.extra_state["sources"]
        )
        if is_done:
            task.extra_state["new_memory"].put(
                ChatMessage(content=agent_response.response, role=MessageRole.ASSISTANT)
            )

        return self._get_task_step_response(agent_response, step, is_done)

    async def _arun_step(
        self,
        step: TaskStep,
        task: Task,
    ) -> TaskStepOutput:
        """Run step."""
        if step.input is not None:
            add_user_step_to_reasoning(
                step,
                task.extra_state["new_memory"],
                task.extra_state["current_reasoning"],
                verbose=self._verbose,
            )
        # TODO: see if we want to do step-based inputs
        tools = self.get_tools(task.input)

        input_chat = self._react_chat_formatter.format(
            tools,
            chat_history=task.memory.get() + task.extra_state["new_memory"].get_all(),
            current_reasoning=task.extra_state["current_reasoning"],
        )
        # send prompt
        chat_response = await self._llm.achat(input_chat)
        # given react prompt outputs, call tools or return response
        reasoning_steps, is_done = await self._aprocess_actions(
            task, tools, output=chat_response
        )
        task.extra_state["current_reasoning"].extend(reasoning_steps)
        agent_response = self._get_response(
            task.extra_state["current_reasoning"], task.extra_state["sources"]
        )
        if is_done:
            task.extra_state["new_memory"].put(
                ChatMessage(content=agent_response.response, role=MessageRole.ASSISTANT)
            )

        return self._get_task_step_response(agent_response, step, is_done)

    def _run_step_stream(
        self,
        step: TaskStep,
        task: Task,
    ) -> TaskStepOutput:
        """Run step."""
        if step.input is not None:
            add_user_step_to_reasoning(
                step,
                task.extra_state["new_memory"],
                task.extra_state["current_reasoning"],
                verbose=self._verbose,
            )
        # TODO: see if we want to do step-based inputs
        tools = self.get_tools(task.input)

        input_chat = self._react_chat_formatter.format(
            tools,
            chat_history=task.memory.get() + task.extra_state["new_memory"].get_all(),
            current_reasoning=task.extra_state["current_reasoning"],
        )

        chat_stream = self._llm.stream_chat(input_chat)

        # iterate over stream, break out if is final answer after the "Answer: "
        full_response = ChatResponse(
            message=ChatMessage(content=None, role="assistant")
        )
        is_done = False
        for latest_chunk in chat_stream:
            full_response = latest_chunk
            is_done = self._infer_stream_chunk_is_final(latest_chunk)
            if is_done:
                break

        if not is_done:
            # given react prompt outputs, call tools or return response
            reasoning_steps, is_done = self._process_actions(
                task, tools=tools, output=full_response, is_streaming=True
            )
            task.extra_state["current_reasoning"].extend(reasoning_steps)
            # use _get_response to return intermediate response
            agent_response: AGENT_CHAT_RESPONSE_TYPE = self._get_response(
                task.extra_state["current_reasoning"], task.extra_state["sources"]
            )
            if is_done:
                agent_response.is_dummy_stream = True
                task.extra_state["new_memory"].put(
                    ChatMessage(
                        content=agent_response.response, role=MessageRole.ASSISTANT
                    )
                )
        else:
            # Get the response in a separate thread so we can yield the response
            response_stream = self._add_back_chunk_to_stream(
                chunk=latest_chunk, chat_stream=chat_stream
            )

            agent_response = StreamingAgentChatResponse(
                chat_stream=response_stream,
                sources=task.extra_state["sources"],
            )
            thread = Thread(
                target=agent_response.write_response_to_history,
                args=(task.extra_state["new_memory"],),
                kwargs={"on_stream_end_fn": partial(self.finalize_task, task)},
            )
            thread.start()

        return self._get_task_step_response(agent_response, step, is_done)

    async def _arun_step_stream(
        self,
        step: TaskStep,
        task: Task,
    ) -> TaskStepOutput:
        """Run step."""
        if step.input is not None:
            add_user_step_to_reasoning(
                step,
                task.extra_state["new_memory"],
                task.extra_state["current_reasoning"],
                verbose=self._verbose,
            )
        # TODO: see if we want to do step-based inputs
        tools = self.get_tools(task.input)

        input_chat = self._react_chat_formatter.format(
            tools,
            chat_history=task.memory.get() + task.extra_state["new_memory"].get_all(),
            current_reasoning=task.extra_state["current_reasoning"],
        )

        chat_stream = await self._llm.astream_chat(input_chat)

        # iterate over stream, break out if is final answer after the "Answer: "
        full_response = ChatResponse(
            message=ChatMessage(content=None, role="assistant")
        )
        is_done = False
        async for latest_chunk in chat_stream:
            full_response = latest_chunk
            is_done = self._infer_stream_chunk_is_final(latest_chunk)
            if is_done:
                break

        if not is_done:
            # given react prompt outputs, call tools or return response
            reasoning_steps, is_done = await self._aprocess_actions(
                task, tools=tools, output=full_response, is_streaming=True
            )
            task.extra_state["current_reasoning"].extend(reasoning_steps)
            # use _get_response to return intermediate response
            agent_response: AGENT_CHAT_RESPONSE_TYPE = self._get_response(
                task.extra_state["current_reasoning"], task.extra_state["sources"]
            )

            if is_done:
                agent_response.is_dummy_stream = True
                task.extra_state["new_memory"].put(
                    ChatMessage(
                        content=agent_response.response, role=MessageRole.ASSISTANT
                    )
                )
        else:
            # Get the response in a separate thread so we can yield the response
            response_stream = self._async_add_back_chunk_to_stream(
                chunk=latest_chunk, chat_stream=chat_stream
            )

            agent_response = StreamingAgentChatResponse(
                achat_stream=response_stream,
                sources=task.extra_state["sources"],
            )
            # create task to write chat response to history
            asyncio.create_task(
                agent_response.awrite_response_to_history(
                    task.extra_state["new_memory"],
                    on_stream_end_fn=partial(self.finalize_task, task),
                )
            )
            # wait until response writing is done
            agent_response._ensure_async_setup()

            await agent_response._is_function_false_event.wait()

        return self._get_task_step_response(agent_response, step, is_done)

    @trace_method("run_step")
    def run_step(self, step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput:
        """Run step."""
        return self._run_step(step, task)

    @trace_method("run_step")
    async def arun_step(
        self, step: TaskStep, task: Task, **kwargs: Any
    ) -> TaskStepOutput:
        """Run step (async)."""
        return await self._arun_step(step, task)

    @trace_method("run_step")
    def stream_step(self, step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput:
        """Run step (stream)."""
        # TODO: figure out if we need a different type for TaskStepOutput
        return self._run_step_stream(step, task)

    @trace_method("run_step")
    async def astream_step(
        self, step: TaskStep, task: Task, **kwargs: Any
    ) -> TaskStepOutput:
        """Run step (async stream)."""
        return await self._arun_step_stream(step, task)

    def finalize_task(self, task: Task, **kwargs: Any) -> None:
        """Finalize task, after all the steps are completed."""
        # add new messages to memory
        task.memory.set(
            task.memory.get_all() + task.extra_state["new_memory"].get_all()
        )
        # reset new memory
        task.extra_state["new_memory"].reset()

    def set_callback_manager(self, callback_manager: CallbackManager) -> None:
        """Set callback manager."""
        # TODO: make this abstractmethod (right now will break some agent impls)
        self.callback_manager = callback_manager

from_tools classmethod

from_tools(tools: Optional[Sequence[BaseTool]] = None, tool_retriever: Optional[ObjectRetriever[BaseTool]] = None, llm: Optional[LLM] = None, max_iterations: int = 10, react_chat_formatter: Optional[ReActChatFormatter] = None, output_parser: Optional[ReActOutputParser] = None, callback_manager: Optional[CallbackManager] = None, verbose: bool = False, handle_reasoning_failure_fn: Optional[Callable[[CallbackManager, Exception], ToolOutput]] = None, **kwargs: Any) -> ReActAgentWorker

Convenience constructor method from set of BaseTools (Optional).

NOTE: kwargs should have been exhausted by this point. In other words the various upstream components such as BaseSynthesizer (response synthesizer) or BaseRetriever should have picked up off their respective kwargs in their constructions.

Returns:

Type	Description
ReActAgentWorker	ReActAgentWorker

Source code in llama-index-core/llama_index/core/agent/react/step.py

@classmethod
def from_tools(
    cls,
    tools: Optional[Sequence[BaseTool]] = None,
    tool_retriever: Optional[ObjectRetriever[BaseTool]] = None,
    llm: Optional[LLM] = None,
    max_iterations: int = 10,
    react_chat_formatter: Optional[ReActChatFormatter] = None,
    output_parser: Optional[ReActOutputParser] = None,
    callback_manager: Optional[CallbackManager] = None,
    verbose: bool = False,
    handle_reasoning_failure_fn: Optional[
        Callable[[CallbackManager, Exception], ToolOutput]
    ] = None,
    **kwargs: Any,
) -> "ReActAgentWorker":
    """Convenience constructor method from set of BaseTools (Optional).

    NOTE: kwargs should have been exhausted by this point. In other words
    the various upstream components such as BaseSynthesizer (response synthesizer)
    or BaseRetriever should have picked up off their respective kwargs in their
    constructions.

    Returns:
        ReActAgentWorker
    """
    llm = llm or Settings.llm
    if callback_manager is not None:
        llm.callback_manager = callback_manager
    return cls(
        tools=tools or [],
        tool_retriever=tool_retriever,
        llm=llm,
        max_iterations=max_iterations,
        react_chat_formatter=react_chat_formatter,
        output_parser=output_parser,
        callback_manager=callback_manager,
        verbose=verbose,
        handle_reasoning_failure_fn=handle_reasoning_failure_fn,
    )

initialize_step

initialize_step(task: Task, **kwargs: Any) -> TaskStep

Initialize step from task.

Source code in llama-index-core/llama_index/core/agent/react/step.py

def initialize_step(self, task: Task, **kwargs: Any) -> TaskStep:
    """Initialize step from task."""
    sources: List[ToolOutput] = []
    current_reasoning: List[BaseReasoningStep] = []
    # temporary memory for new messages
    new_memory = ChatMemoryBuffer.from_defaults()

    # initialize task state
    task_state = {
        "sources": sources,
        "current_reasoning": current_reasoning,
        "new_memory": new_memory,
    }
    task.extra_state.update(task_state)

    return TaskStep(
        task_id=task.task_id,
        step_id=str(uuid.uuid4()),
        input=task.input,
        step_state={"is_first": True},
    )

get_tools

get_tools(input: str) -> List[AsyncBaseTool]

Get tools.

Source code in llama-index-core/llama_index/core/agent/react/step.py

def get_tools(self, input: str) -> List[AsyncBaseTool]:
    """Get tools."""
    return [adapt_to_async_tool(t) for t in self._get_tools(input)]

run_step

run_step(step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput

Run step.

Source code in llama-index-core/llama_index/core/agent/react/step.py

@trace_method("run_step")
def run_step(self, step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput:
    """Run step."""
    return self._run_step(step, task)

arun_step async

arun_step(step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput

Run step (async).

Source code in llama-index-core/llama_index/core/agent/react/step.py

@trace_method("run_step")
async def arun_step(
    self, step: TaskStep, task: Task, **kwargs: Any
) -> TaskStepOutput:
    """Run step (async)."""
    return await self._arun_step(step, task)

stream_step

stream_step(step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput

Run step (stream).

Source code in llama-index-core/llama_index/core/agent/react/step.py

@trace_method("run_step")
def stream_step(self, step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput:
    """Run step (stream)."""
    # TODO: figure out if we need a different type for TaskStepOutput
    return self._run_step_stream(step, task)

astream_step async

astream_step(step: TaskStep, task: Task, **kwargs: Any) -> TaskStepOutput

Run step (async stream).

Source code in llama-index-core/llama_index/core/agent/react/step.py

@trace_method("run_step")
async def astream_step(
    self, step: TaskStep, task: Task, **kwargs: Any
) -> TaskStepOutput:
    """Run step (async stream)."""
    return await self._arun_step_stream(step, task)

finalize_task

finalize_task(task: Task, **kwargs: Any) -> None

Finalize task, after all the steps are completed.

Source code in llama-index-core/llama_index/core/agent/react/step.py

def finalize_task(self, task: Task, **kwargs: Any) -> None:
    """Finalize task, after all the steps are completed."""
    # add new messages to memory
    task.memory.set(
        task.memory.get_all() + task.extra_state["new_memory"].get_all()
    )
    # reset new memory
    task.extra_state["new_memory"].reset()

set_callback_manager

set_callback_manager(callback_manager: CallbackManager) -> None

Set callback manager.

Source code in llama-index-core/llama_index/core/agent/react/step.py

def set_callback_manager(self, callback_manager: CallbackManager) -> None:
    """Set callback manager."""
    # TODO: make this abstractmethod (right now will break some agent impls)
    self.callback_manager = callback_manager

ReActChatFormatter

Bases: BaseAgentChatFormatter

ReAct chat formatter.

Source code in llama-index-core/llama_index/core/agent/react/formatter.py

class ReActChatFormatter(BaseAgentChatFormatter):
    """ReAct chat formatter."""

    system_header: str = REACT_CHAT_SYSTEM_HEADER  # default
    context: str = ""  # not needed w/ default

    def format(
        self,
        tools: Sequence[BaseTool],
        chat_history: List[ChatMessage],
        current_reasoning: Optional[List[BaseReasoningStep]] = None,
    ) -> List[ChatMessage]:
        """Format chat history into list of ChatMessage."""
        current_reasoning = current_reasoning or []

        format_args = {
            "tool_desc": "\n".join(get_react_tool_descriptions(tools)),
            "tool_names": ", ".join([tool.metadata.get_name() for tool in tools]),
        }
        if self.context:
            format_args["context"] = self.context

        fmt_sys_header = self.system_header.format(**format_args)

        # format reasoning history as alternating user and assistant messages
        # where the assistant messages are thoughts and actions and the user
        # messages are observations
        reasoning_history = []
        for reasoning_step in current_reasoning:
            if isinstance(reasoning_step, ObservationReasoningStep):
                message = ChatMessage(
                    role=MessageRole.USER,
                    content=reasoning_step.get_content(),
                )
            else:
                message = ChatMessage(
                    role=MessageRole.ASSISTANT,
                    content=reasoning_step.get_content(),
                )
            reasoning_history.append(message)

        return [
            ChatMessage(role=MessageRole.SYSTEM, content=fmt_sys_header),
            *chat_history,
            *reasoning_history,
        ]

    @classmethod
    def from_defaults(
        cls,
        system_header: Optional[str] = None,
        context: Optional[str] = None,
    ) -> "ReActChatFormatter":
        """Create ReActChatFormatter from defaults."""
        if not system_header:
            system_header = (
                REACT_CHAT_SYSTEM_HEADER
                if not context
                else CONTEXT_REACT_CHAT_SYSTEM_HEADER
            )

        return ReActChatFormatter(
            system_header=system_header,
            context=context or "",
        )

    @classmethod
    def from_context(cls, context: str) -> "ReActChatFormatter":
        """Create ReActChatFormatter from context.

        NOTE: deprecated

        """
        logger.warning(
            "ReActChatFormatter.from_context is deprecated, please use `from_defaults` instead."
        )
        return ReActChatFormatter.from_defaults(
            system_header=CONTEXT_REACT_CHAT_SYSTEM_HEADER, context=context
        )

format

format(tools: Sequence[BaseTool], chat_history: List[ChatMessage], current_reasoning: Optional[List[BaseReasoningStep]] = None) -> List[ChatMessage]

Format chat history into list of ChatMessage.

Source code in llama-index-core/llama_index/core/agent/react/formatter.py

def format(
    self,
    tools: Sequence[BaseTool],
    chat_history: List[ChatMessage],
    current_reasoning: Optional[List[BaseReasoningStep]] = None,
) -> List[ChatMessage]:
    """Format chat history into list of ChatMessage."""
    current_reasoning = current_reasoning or []

    format_args = {
        "tool_desc": "\n".join(get_react_tool_descriptions(tools)),
        "tool_names": ", ".join([tool.metadata.get_name() for tool in tools]),
    }
    if self.context:
        format_args["context"] = self.context

    fmt_sys_header = self.system_header.format(**format_args)

    # format reasoning history as alternating user and assistant messages
    # where the assistant messages are thoughts and actions and the user
    # messages are observations
    reasoning_history = []
    for reasoning_step in current_reasoning:
        if isinstance(reasoning_step, ObservationReasoningStep):
            message = ChatMessage(
                role=MessageRole.USER,
                content=reasoning_step.get_content(),
            )
        else:
            message = ChatMessage(
                role=MessageRole.ASSISTANT,
                content=reasoning_step.get_content(),
            )
        reasoning_history.append(message)

    return [
        ChatMessage(role=MessageRole.SYSTEM, content=fmt_sys_header),
        *chat_history,
        *reasoning_history,
    ]

from_defaults classmethod

from_defaults(system_header: Optional[str] = None, context: Optional[str] = None) -> ReActChatFormatter

Create ReActChatFormatter from defaults.

Source code in llama-index-core/llama_index/core/agent/react/formatter.py

@classmethod
def from_defaults(
    cls,
    system_header: Optional[str] = None,
    context: Optional[str] = None,
) -> "ReActChatFormatter":
    """Create ReActChatFormatter from defaults."""
    if not system_header:
        system_header = (
            REACT_CHAT_SYSTEM_HEADER
            if not context
            else CONTEXT_REACT_CHAT_SYSTEM_HEADER
        )

    return ReActChatFormatter(
        system_header=system_header,
        context=context or "",
    )

from_context classmethod

from_context(context: str) -> ReActChatFormatter

Create ReActChatFormatter from context.

NOTE: deprecated

Source code in llama-index-core/llama_index/core/agent/react/formatter.py

@classmethod
def from_context(cls, context: str) -> "ReActChatFormatter":
    """Create ReActChatFormatter from context.

    NOTE: deprecated

    """
    logger.warning(
        "ReActChatFormatter.from_context is deprecated, please use `from_defaults` instead."
    )
    return ReActChatFormatter.from_defaults(
        system_header=CONTEXT_REACT_CHAT_SYSTEM_HEADER, context=context
    )