feat: Tool dataclass - unified abstraction to represent tools

docs/pydoc/config/data_classess_api.yml

@@ -2,7 +2,7 @@ loaders:
   - type: haystack_pydoc_tools.loaders.CustomPythonLoader
     search_path: [../../../haystack/dataclasses]
     modules:
-      ["answer", "byte_stream", "chat_message", "document", "streaming_chunk", "sparse_embedding"]
+      ["answer", "byte_stream", "chat_message", "document", "streaming_chunk", "sparse_embedding", "tool"]
     ignore_when_discovered: ["__init__"]
 processors:
   - type: filter

haystack/dataclasses/__init__.py

@@ -8,6 +8,7 @@
 from haystack.dataclasses.document import Document
 from haystack.dataclasses.sparse_embedding import SparseEmbedding
 from haystack.dataclasses.streaming_chunk import StreamingChunk
+from haystack.dataclasses.tool import Tool
 
 __all__ = [
     "Document",
@@ -22,4 +23,5 @@
     "TextContent",
     "StreamingChunk",
     "SparseEmbedding",
+    "Tool",
 ]

haystack/dataclasses/tool.py

@@ -0,0 +1,242 @@
+# SPDX-FileCopyrightText: 2022-present deepset GmbH <info@deepset.ai>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import inspect
+from dataclasses import asdict, dataclass
+from typing import Any, Callable, Dict, Optional
+
+from pydantic import create_model
+
+from haystack.lazy_imports import LazyImport
+from haystack.utils import deserialize_callable, serialize_callable
+
+with LazyImport(message="Run 'pip install jsonschema'") as jsonschema_import:
+    from jsonschema import Draft202012Validator
+    from jsonschema.exceptions import SchemaError
+
+
+class ToolInvocationError(Exception):
+    """
+    Exception raised when a Tool invocation fails.
+    """
+
+    pass
+
+
+class SchemaGenerationError(Exception):
+    """
+    Exception raised when automatic schema generation fails.
+    """
+
+    pass
+
+
+@dataclass
+class Tool:
+    """
+    Data class representing a tool for which Language Models can prepare a call.
+
+    Accurate definitions of the textual attributes such as `name` and `description`
+    are important for the Language Model to correctly prepare the call.
+
+    :param name:
+        Name of the tool.
+    :param description:
+        Description of the tool.
+    :param parameters:
+        A JSON schema defining the parameters expected by the tool.
+    :param function:
+        The function that will be invoked when the tool is called.
+    """
+
+    name: str
+    description: str
+    parameters: Dict[str, Any]
+    function: Callable
+
+    def __post_init__(self):
+        jsonschema_import.check()
+        # Check that the parameters define a valid JSON schema
+        try:
+            Draft202012Validator.check_schema(self.parameters)
+        except SchemaError as e:
+            raise ValueError("The provided parameters do not define a valid JSON schema") from e
+
+    @property
+    def tool_spec(self) -> Dict[str, Any]:
+        """
+        Return the tool specification to be used by the Language Model.
+        """
+        return {"name": self.name, "description": self.description, "parameters": self.parameters}
+
+    def invoke(self, **kwargs) -> Any:
+        """
+        Invoke the tool with the provided keyword arguments.
+        """
+
+        try:
+            result = self.function(**kwargs)
+        except Exception as e:
+            raise ToolInvocationError(f"Failed to invoke tool `{self.name}` with parameters {kwargs}") from e
+        return result
+
+    def to_dict(self) -> Dict[str, Any]:
+        """
+        Serializes the Tool to a dictionary.
+
+        :returns:
+            Dictionary with serialized data.
+        """
+
+        serialized = asdict(self)
+        serialized["function"] = serialize_callable(self.function)
+        return serialized
+
+    @classmethod
+    def from_dict(cls, data: Dict[str, Any]) -> "Tool":
+        """
+        Deserializes the Tool from a dictionary.
+
+        :param data:
+            Dictionary to deserialize from.
+        :returns:
+            Deserialized Tool.
+        """
+        data["function"] = deserialize_callable(data["function"])
+        return cls(**data)
+
+    @classmethod
+    def from_function(cls, function: Callable, name: Optional[str] = None, description: Optional[str] = None) -> "Tool":
+        """
+        Create a Tool instance from a function.
+
+        Usage example:
+        ```python
+        from typing import Annotated, Literal
+        from haystack.dataclasses import Tool
+
+        def get_weather(
+            city: Annotated[str, "the city for which to get the weather"] = "Munich",
+            unit: Annotated[Literal["Celsius", "Fahrenheit"], "the unit for the temperature"] = "Celsius"):
+            '''A simple function to get the current weather for a location.'''
+            return f"Weather report for {city}: 20 {unit}, sunny"
+
+        tool = Tool.from_function(get_weather)
+
+        print(tool)
+        >>> Tool(name='get_weather', description='A simple function to get the current weather for a location.',
+        >>> parameters={
+        >>> 'type': 'object',
+        >>> 'properties': {
+        >>>     'city': {'type': 'string', 'description': 'the city for which to get the weather', 'default': 'Munich'},
+        >>>     'unit': {
+        >>>         'type': 'string',
+        >>>         'enum': ['Celsius', 'Fahrenheit'],
+        >>>         'description': 'the unit for the temperature',
+        >>>         'default': 'Celsius',
+        >>>     },
+        >>>     }
+        >>> },
+        >>> function=<function get_weather at 0x7f7b3a8a9b80>)
+        ```
+
+        :param function:
+            The function to be converted into a Tool.
+            The function must include type hints for all parameters.
+            If a parameter is annotated using `typing.Annotated`, its metadata will be used as parameter description.
+        :param name:
+            The name of the tool. If not provided, the name of the function will be used.
+        :param description:
+            The description of the tool. If not provided, the docstring of the function will be used.
+            To intentionally leave the description empty, pass an empty string.
+
+        :returns:
+            The Tool created from the function.
+
+        :raises ValueError:
+            If any parameter of the function lacks a type hint.
+        :raises SchemaGenerationError:
+            If there is an error generating the JSON schema for the Tool.
+        """
+
+        tool_description = description if description is not None else (function.__doc__ or "")
+
+        signature = inspect.signature(function)
+
+        # collect fields (types and defaults) and descriptions from function parameters
+        fields: Dict[str, Any] = {}
+        descriptions = {}
+
+        for param_name, param in signature.parameters.items():
+            if param.annotation is param.empty:
+                raise ValueError(f"Function '{function.__name__}': parameter '{param_name}' does not have a type hint.")
+
+            # if the parameter has not a default value, Pydantic requires an Ellipsis (...)
+            # to explicitly indicate that the parameter is required
+            default = param.default if param.default is not param.empty else ...
+            fields[param_name] = (param.annotation, default)
+
+            if hasattr(param.annotation, "__metadata__"):
+                descriptions[param_name] = param.annotation.__metadata__[0]
+
+        # create Pydantic model and generate JSON schema
+        try:
+            model = create_model(function.__name__, **fields)
+            schema = model.model_json_schema()
+        except Exception as e:
+            raise SchemaGenerationError(f"Failed to create JSON schema for function '{function.__name__}'") from e
+
+        # we don't want to include title keywords in the schema, as they contain redundant information
+        # there is no programmatic way to prevent Pydantic from adding them, so we remove them later
+        # see https://github.com/pydantic/pydantic/discussions/8504
+        _remove_title_from_schema(schema)
+
+        # add parameters descriptions to the schema
+        for param_name, param_description in descriptions.items():
+            if param_name in schema["properties"]:
+                schema["properties"][param_name]["description"] = param_description
+
+        return Tool(name=name or function.__name__, description=tool_description, parameters=schema, function=function)
+
+
+def _remove_title_from_schema(schema: Dict[str, Any]):
+    """
+    Remove the 'title' keyword from JSON schema and contained property schemas.
+
+    :param schema:
+        The JSON schema to remove the 'title' keyword from.
+    """
+    schema.pop("title", None)
+
+    for property_schema in schema["properties"].values():
+        for key in list(property_schema.keys()):
+            if key == "title":
+                del property_schema[key]
+
+
+def deserialize_tools_inplace(data: Dict[str, Any], key: str = "tools"):
+    """
+    Deserialize tools in a dictionary inplace.
+
+    :param data:
+        The dictionary with the serialized data.
+    :param key:
+        The key in the dictionary where the tools are stored.
+    """
+    if key in data:
+        serialized_tools = data[key]
+
+        if serialized_tools is None:
+            return
+
+        if not isinstance(serialized_tools, list):
+            raise TypeError(f"The value of '{key}' is not a list")
+
+        deserialized_tools = []
+        for tool in serialized_tools:
+            if not isinstance(tool, dict):
+                raise TypeError(f"Serialized tool '{tool}' is not a dictionary")
+            deserialized_tools.append(Tool.from_dict(tool))
+
+        data[key] = deserialized_tools

pyproject.toml

@@ -47,6 +47,7 @@ dependencies = [
   "tenacity!=8.4.0",
   "lazy-imports",
   "openai>=1.56.1",
+  "pydantic",
   "Jinja2",
   "posthog",                # telemetry
   "pyyaml",
@@ -113,7 +114,7 @@ extra-dependencies = [
   "jsonref",  # OpenAPIServiceConnector, OpenAPIServiceToFunctions
   "openapi3",
 
-  # Validation
+  # JsonSchemaValidator, Tool
   "jsonschema",
 
   # Tracing

releasenotes/notes/tool-dataclass-12756077bbfea3a1.yaml

@@ -0,0 +1,8 @@
+---
+highlights: >
+    We are introducing the `Tool` dataclass: a simple and unified abstraction to represent tools throughout the framework.
+    By building on this abstraction, we will enable support for tools in Chat Generators,
+    providing a consistent experience across models.
+features:
+  - |
+    Added a new `Tool` dataclass to represent a tool for which Language Models can prepare calls.