Agents

Creating tools

Tools are interfaces that an agent can interact with. You can create custom tools able to perform any functionality you want.

In this example, the Tool is created from a function. The function is the movie_chat.invoke method.

tools = [
    Tool.from_function(
        name="Movie Chat",
        description="For when you need to chat about movies. The question will be a string. Return a string.",
        func=movie_chat.invoke,
    )
]

The name and description help the LLM select which tool to use when presented with a question. The func parameter is the function that will be called when the tool is selected. The return_direct flag indicates that the tool will return the result directly.

Agents support multiple tools, so you pass them to the agent as a list (tools).

Initializing an agent

The following code creates the agent:

agent_prompt = hub.pull("hwchase17/react-chat")
agent = create_react_agent(llm, tools, agent_prompt)
agent_executor = AgentExecutor(agent=agent, tools=tools)

There are different types of agents that you can create. This example creates a ReAct - Reasoning and Acting) agent type.

An agent requires a prompt. You could create a prompt, but in this example, the program pulls a pre-existing prompt from the Langsmith Hub.

The hwcase17/react-chat prompt instructs the model to provide an answer using the tools available in a specific format.

The create_react_agent function creates the agent and expects the following parameters:

The AgentExecutor class runs the agent. It expects the following parameters:

agent_executor = AgentExecutor(
    agent=agent,
    tools=tools,
    max_iterations=3,
    verbose=True,
    handle_parse_errors=True
)

Multiple tools

A key advantage of using an agent is that they can use multiple tools. Access to multiple tools allows you to create agents that can perform several specific tasks.

You can extend this example to allow it to search YouTube for movie trailers by adding the YouTube Tool to the tools list.

Firstly, you will need to install the youtube-search package.

pip install youtube-search

Import the YouTubeSearchTool and create a new tool.

from langchain_community.tools import YouTubeSearchTool

youtube = YouTubeSearchTool()

The YouTubeSearchTool tool expects a search term and the number of results passed as a comma-separated string.

The agent may pass queries containing commas, so create a function to strip the commas from the query and pass the query to the YouTubeSearchTool.

def call_trailer_search(input):
    input = input.replace(",", " ")
    return youtube.run(input)

Finally, add the call_trailer_search function to the tools list.

tools = [
    Tool.from_function(
        name="Movie Chat",
        description="For when you need to chat about movies. The question will be a string. Return a string.",
        func=movie_chat.invoke,
    ),
    Tool.from_function(
        name="Movie Trailer Search",
        description="Use when needing to find a movie trailer. The question will include the word trailer. Return a link to a YouTube video.",
        func=call_trailer_search,
    ),
]

from langchain_openai import ChatOpenAI
from langchain.agents import AgentExecutor, create_react_agent
from langchain.tools import Tool
from langchain import hub
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain.schema import StrOutputParser
from langchain_community.tools import YouTubeSearchTool
from langchain_neo4j import Neo4jChatMessageHistory, Neo4jGraph
from uuid import uuid4

SESSION_ID = str(uuid4())
print(f"Session ID: {SESSION_ID}")

llm = ChatOpenAI(openai_api_key="sk-...")

graph = Neo4jGraph(
    url="bolt://localhost:7687",
    username="neo4j",
    password="pleaseletmein"
)

prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You are a movie expert. You find movies from a genre or plot.",
        ),
        ("human", "{input}"),
    ]
)

movie_chat = prompt | llm | StrOutputParser()

youtube = YouTubeSearchTool()

def get_memory(session_id):
    return Neo4jChatMessageHistory(session_id=session_id, graph=graph)

def call_trailer_search(input):
    input = input.replace(",", " ")
    return youtube.run(input)

tools = [
    Tool.from_function(
        name="Movie Chat",
        description="For when you need to chat about movies. The question will be a string. Return a string.",
        func=movie_chat.invoke,
    ),
    Tool.from_function(
        name="Movie Trailer Search",
        description="Use when needing to find a movie trailer. The question will include the word trailer. Return a link to a YouTube video.",
        func=call_trailer_search,
    ),
]

agent_prompt = hub.pull("hwchase17/react-chat")
agent = create_react_agent(llm, tools, agent_prompt)
agent_executor = AgentExecutor(agent=agent, tools=tools)

chat_agent = RunnableWithMessageHistory(
    agent_executor,
    get_memory,
    input_messages_key="input",
    history_messages_key="chat_history",
)

while True:
    q = input("> ")

    response = chat_agent.invoke(
        {
            "input": q
        },
        {"configurable": {"session_id": SESSION_ID}},
    )
    
    print(response["output"])

The model will use the name and description for each tool to decide which tool to use.

When prompted to find a movie trailer, the model should use the YouTubeSearchTool tool.

[user] Find the movie trailer for the Matrix.

[agent] Here are the movie trailers for "The Matrix":

The Matrix - Official Trailer #1 -
    https://www.youtube.com/watch?v=vKQi3bBA1y8&pp=ygUKVGhlIE1hdHJpeA%3D%3D

The Matrix - Official Trailer #2 -
    https://www.youtube.com/watch?v=xrYg_qKX-aI&pp=ygUKVGhlIE1hdHJpeA%3D%3D

However, when asked about movies, genres or plots, the model will use the chat_chain tool.

[user] Find a movie about the meaning of life

[agent] Certainly! One movie that explores the meaning of life is "The Tree of Life" directed by Terrence Malick. It follows the journey of a young boy as he grows up in the 1950s and reflects on his experiences and the meaning of existence. It's a visually stunning and thought-provoking film that delves into existential questions.

As the agent also uses the conversation memory, you can refer back to the previous questions, such as finding a trailer for a movie it has recommended:

[user] Can you find the trailer

[agent] Here are two links to the trailer for "The Tree of Life":

Link 1 - https://www.youtube.com/watch?v=RrAz1YLh8nY&pp=ygUQVGhlIFRyZWUgb2YgTGlmZQ%3D%3D

Link 2 - https://www.youtube.com/watch?v=cv-dH5gHi1c&pp=ygUQVGhlIFRyZWUgb2YgTGlmZQ%3D%3D

Agents and tools allow you to create more adaptable and flexible models to perform multiple tasks.