FunctionTool

The FunctionTool class is a specialized Tool designed to invoke custom function-based operations within event-driven workflows. It provides a flexible framework for integrating arbitrary function logic, allowing developers to wrap any callable function and seamlessly integrate it into the workflow system. The tool handles both synchronous and asynchronous function execution while maintaining compatibility with the broader tool interface.

Fields

Field	Type	Description
`name`	`str`	Human-readable name identifying the function tool (defaults to `"FunctionTool"`).
`type`	`str`	Specifies the type of the tool (set to `"FunctionTool"`).
`function`	`Callable[[Messages], OutputType]`	The callable function that processes input messages and returns output data.
`oi_span_type`	`OpenInferenceSpanKindValues`	Semantic attribute from OpenInference used for tracing (set to `TOOL`).

Methods

Method	Signature	Description
`builder()`	`classmethod -> FunctionToolBuilder`	Returns a builder instance for constructing FunctionTool objects.
`invoke`	`(invoke_context: InvokeContext, input_data: Messages) -> Messages`	Synchronously invokes the wrapped function with input messages and returns the result as messages.
`a_invoke`	`async (invoke_context: InvokeContext, input_data: Messages) -> MsgsAGen`	Asynchronously invokes the function, supporting both regular and await-able functions.
`to_messages`	`(response: OutputType) -> Messages`	Converts the function's raw response into standardized `Message` objects with appropriate formatting.
`to_dict`	`() -> dict[str, Any]`	Serializes the tool's configuration into a dictionary format for persistence or debugging.

Usage and Customization

Function Requirements

The FunctionTool can wrap any callable that accepts a Messages list as input and returns various output types. The function signature must be:

def your_function(messages: Messages) -> OutputType

Where OutputType is defined as Union[BaseModel, List[BaseModel]] but the tool also supports additional types through its output handling.

Output Handling

The tool automatically handles different response types in its to_messages method:

BaseModel instances: Serialized to JSON using model_dump_json()
Lists of BaseModel objects: Converted to JSON arrays using model_dump() for each item
String responses: Used directly as message content
Other types: Encoded using jsonpickle for complex object serialization

Async Support

The a_invoke method supports both synchronous and asynchronous functions:

For regular functions: Executes the function normally
For async functions: Automatically detects await-able responses using inspect.isawaitable() and awaits them
Returns results as an async generator (MsgsAGen)

Builder Pattern

The FunctionTool uses a builder pattern for construction through the FunctionToolBuilder class:

function_tool = (
    FunctionTool.builder()
    .function(your_custom_function)
    .build()
)

Example Usage

from grafi.tools.functions.function_tool import FunctionTool
from grafi.common.models.message import Messages
from pydantic import BaseModel

class ProcessResult(BaseModel):
    status: str
    data: dict

def my_custom_function(messages: Messages) -> ProcessResult:
    # Process the input messages
    content = messages[0].content if messages else ""

    return ProcessResult(
        status="processed",
        data={"input_length": len(content)}
    )

# Build the tool
function_tool = (
    FunctionTool.builder()
    .function(my_custom_function)
    .build()
)

Decorators

The FunctionTool class uses the @use_command(Command) decorator, which enables integration with the command pattern for tool execution within the workflow system.

By providing a consistent interface for function execution, the FunctionTool enables developers to integrate custom computational logic into event-driven workflows while maintaining clean separation between workflow orchestration and business logic implementation.