Introduction to Custom Tools in LangChain

LangChain is a versatile Python library that simplifies the process of building applications with large language models (LLMs). One of its most powerful features is the ability to create custom tools, which allow you to extend the capabilities of your AI systems. In this blog post, we'll explore how to harness the power of custom tools and function calling in LangChain.

Why Use Custom Tools?

Custom tools in LangChain enable you to:

1. Add domain-specific functionalities to your AI applications
2. Integrate external APIs and services seamlessly
3. Enhance the reasoning capabilities of your language models
4. Create more interactive and dynamic AI-powered systems

Creating Your First Custom Tool

Let's start by creating a simple custom tool in LangChain. We'll build a tool that converts temperatures between Celsius and Fahrenheit.

from langchain.tools import BaseTool
from pydantic import BaseModel, Field

class TemperatureInput(BaseModel):
    temperature: float = Field(description="The temperature to convert")
    unit: str = Field(description="The unit of the input temperature (C or F)")

class TemperatureConverter(BaseTool):
    name = "temperature_converter"
    description = "Converts temperatures between Celsius and Fahrenheit"
    args_schema = TemperatureInput

    def _run(self, temperature: float, unit: str):
        if unit.upper() == 'C':
            result = (temperature * 9/5) + 32
            return f"{temperature}°C is equal to {result:.2f}°F"
        elif unit.upper() == 'F':
            result = (temperature - 32) * 5/9
            return f"{temperature}°F is equal to {result:.2f}°C"
        else:
            return "Invalid unit. Please use 'C' for Celsius or 'F' for Fahrenheit."

    def _arun(self, temperature: float, unit: str):
        # For async implementation
        raise NotImplementedError("TemperatureConverter does not support async")

In this example, we've created a TemperatureConverter tool that inherits from BaseTool. We've defined the input schema using Pydantic models and implemented the _run method to perform the conversion.

Integrating Custom Tools with LangChain Agents

Now that we have our custom tool, let's see how to integrate it with a LangChain agent:

from langchain.agents import initialize_agent, Tool
from langchain.llms import OpenAI

llm = OpenAI(temperature=0)

tools = [
    Tool(
        name="TemperatureConverter",
        func=TemperatureConverter().run,
        description="Useful for converting temperatures between Celsius and Fahrenheit"
    )
]

agent = initialize_agent(tools, llm, agent="zero-shot-react-description", verbose=True)

result = agent.run("Convert 25 degrees Celsius to Fahrenheit")
print(result)

This code snippet demonstrates how to create an agent that can use our custom temperature conversion tool.

Function Calling in LangChain

Function calling is another powerful feature in LangChain that allows you to define specific functions that language models can use. This capability enables more structured and predictable outputs from your AI systems.

Let's create a simple function that calculates the area of a circle:

import math
from langchain.llms import OpenAI
from langchain.prompts import PromptTemplate
from langchain.chains import LLMChain

def calculate_circle_area(radius: float) -> float:
    return math.pi * radius ** 2

llm = OpenAI(temperature=0)

prompt = PromptTemplate(
    input_variables=["radius"],
    template="The area of a circle with radius {radius} is {area:.2f} square units."
)

chain = LLMChain(llm=llm, prompt=prompt)

radius = 5
area = calculate_circle_area(radius)
result = chain.run(radius=radius, area=area)
print(result)

In this example, we've defined a calculate_circle_area function and used it in conjunction with an LLMChain to generate a natural language response about the area of a circle.

Combining Custom Tools and Function Calling

The real power of LangChain comes from combining custom tools and function calling. Let's create a more complex example that uses both:

from langchain.tools import BaseTool
from langchain.agents import initialize_agent, Tool
from langchain.llms import OpenAI
from pydantic import BaseModel, Field
import math

class CircleInput(BaseModel):
    radius: float = Field(description="The radius of the circle")

class CircleCalculator(BaseTool):
    name = "circle_calculator"
    description = "Calculates various properties of a circle"
    args_schema = CircleInput

    def _run(self, radius: float):
        area = math.pi * radius ** 2
        circumference = 2 * math.pi * radius
        return f"For a circle with radius {radius}:\nArea: {area:.2f}\nCircumference: {circumference:.2f}"

    def _arun(self, radius: float):
        raise NotImplementedError("CircleCalculator does not support async")

llm = OpenAI(temperature=0)

tools = [
    Tool(
        name="CircleCalculator",
        func=CircleCalculator().run,
        description="Useful for calculating properties of a circle given its radius"
    )
]

agent = initialize_agent(tools, llm, agent="zero-shot-react-description", verbose=True)

result = agent.run("What are the area and circumference of a circle with radius 7?")
print(result)

This example combines a custom tool (CircleCalculator) with function calling capabilities, allowing the agent to perform complex calculations and provide informative responses about circle properties.

Best Practices for Custom Tools and Function Calling

1. Keep your tools and functions focused on specific tasks
2. Provide clear descriptions and input schemas for your tools
3. Handle edge cases and potential errors gracefully
4. Use type hints and Pydantic models for better code clarity and validation
5. Leverage async capabilities when dealing with I/O-bound operations

Conclusion

Custom tools and function calling in LangChain open up a world of possibilities for creating powerful and flexible AI applications. By combining these features, you can build sophisticated systems that leverage the strengths of language models while incorporating your own domain-specific knowledge and functionalities.