Workflow for a ReAct Agent¶

This notebook walks through setting up a Workflow to construct a ReAct agent from (mostly) scratch.

React calling agents work by prompting an LLM to either invoke tools/functions, or return a final response.

Our workflow will be stateful with memory, and will be able to call the LLM to select tools and process incoming user messages.

In [ ]:

!pip install -U llama-index

!pip install -U llama-index

In [ ]:

import os

os.environ["OPENAI_API_KEY"] = "sk-proj--..."

import os os.environ["OPENAI_API_KEY"] = "sk-proj--..."

[Optional] Set up observability with Llamatrace¶

Set up tracing to visualize each step in the workflow.

In [ ]:

!pip install "llama-index-core>=0.10.43" "openinference-instrumentation-llama-index>=2" "opentelemetry-proto>=1.12.0" opentelemetry-exporter-otlp opentelemetry-sdk

!pip install "llama-index-core>=0.10.43" "openinference-instrumentation-llama-index>=2" "opentelemetry-proto>=1.12.0" opentelemetry-exporter-otlp opentelemetry-sdk

In [ ]:

from opentelemetry.sdk import trace as trace_sdk
from opentelemetry.sdk.trace.export import SimpleSpanProcessor
from opentelemetry.exporter.otlp.proto.http.trace_exporter import (
    OTLPSpanExporter as HTTPSpanExporter,
)
from openinference.instrumentation.llama_index import LlamaIndexInstrumentor


# Add Phoenix API Key for tracing
PHOENIX_API_KEY = "<YOUR-PHOENIX-API-KEY>"
os.environ["OTEL_EXPORTER_OTLP_HEADERS"] = f"api_key={PHOENIX_API_KEY}"

# Add Phoenix
span_phoenix_processor = SimpleSpanProcessor(
    HTTPSpanExporter(endpoint="https://app.phoenix.arize.com/v1/traces")
)

# Add them to the tracer
tracer_provider = trace_sdk.TracerProvider()
tracer_provider.add_span_processor(span_processor=span_phoenix_processor)

# Instrument the application
LlamaIndexInstrumentor().instrument(tracer_provider=tracer_provider)

from opentelemetry.sdk import trace as trace_sdk from opentelemetry.sdk.trace.export import SimpleSpanProcessor from opentelemetry.exporter.otlp.proto.http.trace_exporter import ( OTLPSpanExporter as HTTPSpanExporter, ) from openinference.instrumentation.llama_index import LlamaIndexInstrumentor # Add Phoenix API Key for tracing PHOENIX_API_KEY = "" os.environ["OTEL_EXPORTER_OTLP_HEADERS"] = f"api_key={PHOENIX_API_KEY}" # Add Phoenix span_phoenix_processor = SimpleSpanProcessor( HTTPSpanExporter(endpoint="https://app.phoenix.arize.com/v1/traces") ) # Add them to the tracer tracer_provider = trace_sdk.TracerProvider() tracer_provider.add_span_processor(span_processor=span_phoenix_processor) # Instrument the application LlamaIndexInstrumentor().instrument(tracer_provider=tracer_provider)

Since workflows are async first, this all runs fine in a notebook. If you were running in your own code, you would want to use asyncio.run() to start an async event loop if one isn't already running.

async def main():
    <async code>

if __name__ == "__main__":
    import asyncio
    asyncio.run(main())

Designing the Workflow¶

An agent consists of several steps

1. Handling the latest incoming user message, including adding to memory and preparing the chat history
2. Using the chat history and tools to construct a ReAct prompt
3. Calling the llm with the react prompt, and parsing out function/tool calls
4. If no tool calls, we can return
5. If there are tool calls, we need to execute them, and then loop back for a fresh ReAct prompt using the latest tool calls

The Workflow Events¶

To handle these steps, we need to define a few events:

1. An event to handle new messages and prepare the chat history
2. An event to prompt the LLM with the react prompt
3. An event to trigger tool calls, if any
4. An event to handle the results of tool calls, if any

The other steps will use the built-in StartEvent and StopEvent events.

In addition to events, we will also use the global context to store the current react reasoning!

In [ ]:

from llama_index.core.llms import ChatMessage
from llama_index.core.tools import ToolSelection, ToolOutput
from llama_index.core.workflow import Event


class PrepEvent(Event):
    pass


class InputEvent(Event):
    input: list[ChatMessage]


class ToolCallEvent(Event):
    tool_calls: list[ToolSelection]


class FunctionOutputEvent(Event):
    output: ToolOutput

from llama_index.core.llms import ChatMessage from llama_index.core.tools import ToolSelection, ToolOutput from llama_index.core.workflow import Event class PrepEvent(Event): pass class InputEvent(Event): input: list[ChatMessage] class ToolCallEvent(Event): tool_calls: list[ToolSelection] class FunctionOutputEvent(Event): output: ToolOutput

The Workflow Itself¶

With our events defined, we can construct our workflow and steps.

Note that the workflow automatically validates itself using type annotations, so the type annotations on our steps are very helpful!

In [ ]:

from typing import Any, List

from llama_index.core.agent.react import ReActChatFormatter, ReActOutputParser
from llama_index.core.agent.react.types import (
    ActionReasoningStep,
    ObservationReasoningStep,
)
from llama_index.core.llms.llm import LLM
from llama_index.core.memory import ChatMemoryBuffer
from llama_index.core.tools.types import BaseTool
from llama_index.core.workflow import (
    Context,
    Workflow,
    StartEvent,
    StopEvent,
    step,
)
from llama_index.llms.openai import OpenAI


class ReActAgent(Workflow):
    def __init__(
        self,
        *args: Any,
        llm: LLM | None = None,
        tools: list[BaseTool] | None = None,
        extra_context: str | None = None,
        **kwargs: Any,
    ) -> None:
        super().__init__(*args, **kwargs)
        self.tools = tools or []

        self.llm = llm or OpenAI()

        self.memory = ChatMemoryBuffer.from_defaults(llm=llm)
        self.formatter = ReActChatFormatter(context=extra_context or "")
        self.output_parser = ReActOutputParser()
        self.sources = []

    @step
    async def new_user_msg(self, ctx: Context, ev: StartEvent) -> PrepEvent:
        # clear sources
        self.sources = []

        # get user input
        user_input = ev.input
        user_msg = ChatMessage(role="user", content=user_input)
        self.memory.put(user_msg)

        # clear current reasoning
        await ctx.set("current_reasoning", [])

        return PrepEvent()

    @step
    async def prepare_chat_history(
        self, ctx: Context, ev: PrepEvent
    ) -> InputEvent:
        # get chat history
        chat_history = self.memory.get()
        current_reasoning = await ctx.get("current_reasoning", default=[])
        llm_input = self.formatter.format(
            self.tools, chat_history, current_reasoning=current_reasoning
        )
        return InputEvent(input=llm_input)

    @step
    async def handle_llm_input(
        self, ctx: Context, ev: InputEvent
    ) -> ToolCallEvent | StopEvent:
        chat_history = ev.input

        response = await self.llm.achat(chat_history)

        try:
            reasoning_step = self.output_parser.parse(response.message.content)
            (await ctx.get("current_reasoning", default=[])).append(
                reasoning_step
            )
            if reasoning_step.is_done:
                self.memory.put(
                    ChatMessage(
                        role="assistant", content=reasoning_step.response
                    )
                )
                return StopEvent(
                    result={
                        "response": reasoning_step.response,
                        "sources": [*self.sources],
                        "reasoning": await ctx.get(
                            "current_reasoning", default=[]
                        ),
                    }
                )
            elif isinstance(reasoning_step, ActionReasoningStep):
                tool_name = reasoning_step.action
                tool_args = reasoning_step.action_input
                return ToolCallEvent(
                    tool_calls=[
                        ToolSelection(
                            tool_id="fake",
                            tool_name=tool_name,
                            tool_kwargs=tool_args,
                        )
                    ]
                )
        except Exception as e:
            (await ctx.get("current_reasoning", default=[])).append(
                ObservationReasoningStep(
                    observation=f"There was an error in parsing my reasoning: {e}"
                )
            )

        # if no tool calls or final response, iterate again
        return PrepEvent()

    @step
    async def handle_tool_calls(
        self, ctx: Context, ev: ToolCallEvent
    ) -> PrepEvent:
        tool_calls = ev.tool_calls
        tools_by_name = {tool.metadata.get_name(): tool for tool in self.tools}

        # call tools -- safely!
        for tool_call in tool_calls:
            tool = tools_by_name.get(tool_call.tool_name)
            if not tool:
                (await ctx.get("current_reasoning", default=[])).append(
                    ObservationReasoningStep(
                        observation=f"Tool {tool_call.tool_name} does not exist"
                    )
                )
                continue

            try:
                tool_output = tool(**tool_call.tool_kwargs)
                self.sources.append(tool_output)
                (await ctx.get("current_reasoning", default=[])).append(
                    ObservationReasoningStep(observation=tool_output.content)
                )
            except Exception as e:
                (await ctx.get("current_reasoning", default=[])).append(
                    ObservationReasoningStep(
                        observation=f"Error calling tool {tool.metadata.get_name()}: {e}"
                    )
                )

        # prep the next iteraiton
        return PrepEvent()

from typing import Any, List from llama_index.core.agent.react import ReActChatFormatter, ReActOutputParser from llama_index.core.agent.react.types import ( ActionReasoningStep, ObservationReasoningStep, ) from llama_index.core.llms.llm import LLM from llama_index.core.memory import ChatMemoryBuffer from llama_index.core.tools.types import BaseTool from llama_index.core.workflow import ( Context, Workflow, StartEvent, StopEvent, step, ) from llama_index.llms.openai import OpenAI class ReActAgent(Workflow): def __init__( self, *args: Any, llm: LLM | None = None, tools: list[BaseTool] | None = None, extra_context: str | None = None, **kwargs: Any, ) -> None: super().__init__(*args, **kwargs) self.tools = tools or [] self.llm = llm or OpenAI() self.memory = ChatMemoryBuffer.from_defaults(llm=llm) self.formatter = ReActChatFormatter(context=extra_context or "") self.output_parser = ReActOutputParser() self.sources = [] @step async def new_user_msg(self, ctx: Context, ev: StartEvent) -> PrepEvent: # clear sources self.sources = [] # get user input user_input = ev.input user_msg = ChatMessage(role="user", content=user_input) self.memory.put(user_msg) # clear current reasoning await ctx.set("current_reasoning", []) return PrepEvent() @step async def prepare_chat_history( self, ctx: Context, ev: PrepEvent ) -> InputEvent: # get chat history chat_history = self.memory.get() current_reasoning = await ctx.get("current_reasoning", default=[]) llm_input = self.formatter.format( self.tools, chat_history, current_reasoning=current_reasoning ) return InputEvent(input=llm_input) @step async def handle_llm_input( self, ctx: Context, ev: InputEvent ) -> ToolCallEvent | StopEvent: chat_history = ev.input response = await self.llm.achat(chat_history) try: reasoning_step = self.output_parser.parse(response.message.content) (await ctx.get("current_reasoning", default=[])).append( reasoning_step ) if reasoning_step.is_done: self.memory.put( ChatMessage( role="assistant", content=reasoning_step.response ) ) return StopEvent( result={ "response": reasoning_step.response, "sources": [*self.sources], "reasoning": await ctx.get( "current_reasoning", default=[] ), } ) elif isinstance(reasoning_step, ActionReasoningStep): tool_name = reasoning_step.action tool_args = reasoning_step.action_input return ToolCallEvent( tool_calls=[ ToolSelection( tool_id="fake", tool_name=tool_name, tool_kwargs=tool_args, ) ] ) except Exception as e: (await ctx.get("current_reasoning", default=[])).append( ObservationReasoningStep( observation=f"There was an error in parsing my reasoning: {e}" ) ) # if no tool calls or final response, iterate again return PrepEvent() @step async def handle_tool_calls( self, ctx: Context, ev: ToolCallEvent ) -> PrepEvent: tool_calls = ev.tool_calls tools_by_name = {tool.metadata.get_name(): tool for tool in self.tools} # call tools -- safely! for tool_call in tool_calls: tool = tools_by_name.get(tool_call.tool_name) if not tool: (await ctx.get("current_reasoning", default=[])).append( ObservationReasoningStep( observation=f"Tool {tool_call.tool_name} does not exist" ) ) continue try: tool_output = tool(**tool_call.tool_kwargs) self.sources.append(tool_output) (await ctx.get("current_reasoning", default=[])).append( ObservationReasoningStep(observation=tool_output.content) ) except Exception as e: (await ctx.get("current_reasoning", default=[])).append( ObservationReasoningStep( observation=f"Error calling tool {tool.metadata.get_name()}: {e}" ) ) # prep the next iteraiton return PrepEvent()

And thats it! Let's explore the workflow we wrote a bit.

new_user_msg(): Adds the user message to memory, and clears the global context to keep track of a fresh string of reasoning.

prepare_chat_history(): Prepares the react prompt, using the chat history, tools, and current reasoning (if any)

handle_llm_input(): Prompts the LLM with our react prompt, and uses some utility functions to parse the output. If there are no tool calls, we can stop and emit a StopEvent. Otherwise, we emit a ToolCallEvent to handle tool calls. Lastly, if there are no tool calls, and no final response, we simply loop again.

handle_tool_calls(): Safely calls tools with error handling, adding the tool outputs to the current reasoning. Then, by emitting a PrepEvent, we loop around for another round of ReAct prompting and parsing.

Run the Workflow!¶

NOTE: With loops, we need to be mindful of runtime. Here, we set a timeout of 120s.

In [ ]:

from llama_index.core.tools import FunctionTool
from llama_index.llms.openai import OpenAI


def add(x: int, y: int) -> int:
    """Useful function to add two numbers."""
    return x + y


def multiply(x: int, y: int) -> int:
    """Useful function to multiply two numbers."""
    return x * y


tools = [
    FunctionTool.from_defaults(add),
    FunctionTool.from_defaults(multiply),
]

agent = ReActAgent(
    llm=OpenAI(model="gpt-4o-mini"), tools=tools, timeout=120, verbose=True
)

ret = await agent.run(input="Hello!")

from llama_index.core.tools import FunctionTool from llama_index.llms.openai import OpenAI def add(x: int, y: int) -> int: """Useful function to add two numbers.""" return x + y def multiply(x: int, y: int) -> int: """Useful function to multiply two numbers.""" return x * y tools = [ FunctionTool.from_defaults(add), FunctionTool.from_defaults(multiply), ] agent = ReActAgent( llm=OpenAI(model="gpt-4o-mini"), tools=tools, timeout=120, verbose=True ) ret = await agent.run(input="Hello!")

Running step new_user_msg
Step new_user_msg produced event PrepEvent
Running step prepare_chat_history
Step prepare_chat_history produced event InputEvent
Running step handle_llm_input
Step handle_llm_input produced event StopEvent

In [ ]:

print(ret["response"])

print(ret["response"])

Hello! How can I assist you today?
```

In [ ]:

ret = await agent.run(input="What is (2123 + 2321) * 312?")

ret = await agent.run(input="What is (2123 + 2321) * 312?")

Running step new_user_msg
Step new_user_msg produced event PrepEvent
Running step prepare_chat_history
Step prepare_chat_history produced event InputEvent
Running step handle_llm_input

Step handle_llm_input produced event ToolCallEvent
Running step handle_tool_calls
Step handle_tool_calls produced event PrepEvent
Running step prepare_chat_history
Step prepare_chat_history produced event InputEvent
Running step handle_llm_input
Step handle_llm_input produced event ToolCallEvent
Running step handle_tool_calls
Step handle_tool_calls produced event PrepEvent
Running step prepare_chat_history
Step prepare_chat_history produced event InputEvent
Running step handle_llm_input
Step handle_llm_input produced event StopEvent

In [ ]:

print(ret["response"])

print(ret["response"])

The result of (2123 + 2321) * 312 is 1,386,528.