Dynamic tool -> single purpose (#3697)

I think the logic of
https://github.com/hwchase17/langchain/pull/3684#pullrequestreview-1405358565
is too confusing.

I prefer this alternative because:
- All `Tool()` implementations by default will be treated the same as
before. No breaking changes.
- Less reliance on pydantic magic
- The decorator (which only is typed as returning a callable) can infer
schema and generate a structured tool
- Either way, the recommended way to create a custom tool is through
inheriting from the base tool

langchain/agents/tools.py

@@ -1,15 +1,10 @@
 """Interface for tools."""
 from functools import partial
-from inspect import signature
-from typing import Any, Awaitable, Callable, Optional, Type, Union
+from typing import Any, Awaitable, Callable, Dict, Optional, Tuple, Type, Union
 
-from pydantic import BaseModel, validate_arguments, validator
+from pydantic import BaseModel, validator
 
-from langchain.tools.base import (
-    BaseTool,
-    create_schema_from_function,
-    get_filtered_args,
-)
+from langchain.tools.base import BaseTool, StructuredTool
 
 
 class Tool(BaseTool):
@@ -30,17 +25,30 @@ class Tool(BaseTool):
 
     @property
     def args(self) -> dict:
+        """The tool's input arguments."""
         if self.args_schema is not None:
             return self.args_schema.schema()["properties"]
-        else:
-            inferred_model = validate_arguments(self.func).model  # type: ignore
-            return get_filtered_args(inferred_model, self.func)
+        # For backwards compatibility, if the function signature is ambiguous,
+        # assume it takes a single string input.
+        return {"tool_input": {"type": "string"}}
+
+    def _to_args_and_kwargs(self, tool_input: Union[str, Dict]) -> Tuple[Tuple, Dict]:
+        """Convert tool input to pydantic model."""
+        args, kwargs = super()._to_args_and_kwargs(tool_input)
+        # For backwards compatibility. The tool must be run with a single input
+        all_args = list(args) + list(kwargs.values())
+        if len(all_args) != 1:
+            raise ValueError(
+                f"Too many arguments to single-input tool {self.name}."
+                f" Args: {all_args}"
+            )
+        return tuple(all_args), {}
 
-    def _run(self, *args: Any, **kwargs: Any) -> str:
+    def _run(self, *args: Any, **kwargs: Any) -> Any:
         """Use the tool."""
         return self.func(*args, **kwargs)
 
-    async def _arun(self, *args: Any, **kwargs: Any) -> str:
+    async def _arun(self, *args: Any, **kwargs: Any) -> Any:
         """Use the tool asynchronously."""
         if self.coroutine:
             return await self.coroutine(*args, **kwargs)
@@ -48,7 +56,7 @@ class Tool(BaseTool):
 
     # TODO: this is for backwards compatibility, remove in future
     def __init__(
-        self, name: str, func: Callable[[str], str], description: str, **kwargs: Any
+        self, name: str, func: Callable, description: str, **kwargs: Any
     ) -> None:
         """Initialize tool."""
         super(Tool, self).__init__(
@@ -107,22 +115,24 @@ def tool(
     """
 
     def _make_with_name(tool_name: str) -> Callable:
-        def _make_tool(func: Callable) -> Tool:
-            assert func.__doc__, "Function must have a docstring"
-            # Description example:
-            # search_api(query: str) - Searches the API for the query.
-            description = f"{tool_name}{signature(func)} - {func.__doc__.strip()}"
-            _args_schema = args_schema
-            if _args_schema is None and infer_schema:
-                _args_schema = create_schema_from_function(f"{tool_name}Schema", func)
-            tool_ = Tool(
+        def _make_tool(func: Callable) -> BaseTool:
+            if infer_schema or args_schema is not None:
+                return StructuredTool.from_function(
+                    func,
+                    name=tool_name,
+                    return_direct=return_direct,
+                    args_schema=args_schema,
+                    infer_schema=infer_schema,
+                )
+            # If someone doesn't want a schema applied, we must treat it as
+            # a simple string->string function
+            assert func.__doc__ is not None, "Function must have a docstring"
+            return Tool(
                 name=tool_name,
                 func=func,
-                args_schema=_args_schema,
-                description=description,
+                description=f"{tool_name} tool",
                 return_direct=return_direct,
             )
-            return tool_
 
         return _make_tool
 

langchain/tools/base.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 
 from abc import ABC, abstractmethod
 from inspect import signature
-from typing import Any, Callable, Dict, Optional, Sequence, Tuple, Type, Union
+from typing import Any, Awaitable, Callable, Dict, Optional, Tuple, Type, Union
 
 from pydantic import (
     BaseModel,
@@ -19,15 +19,6 @@ from langchain.callbacks import get_callback_manager
 from langchain.callbacks.base import BaseCallbackManager
 
 
-def _to_args_and_kwargs(run_input: Union[str, Dict]) -> Tuple[Sequence, dict]:
-    # For backwards compatability, if run_input is a string,
-    # pass as a positional argument.
-    if isinstance(run_input, str):
-        return (run_input,), {}
-    else:
-        return [], run_input
-
-
 class SchemaAnnotationError(TypeError):
     """Raised when 'args_schema' is missing or has an incorrect type annotation."""
 
@@ -81,14 +72,20 @@ def _create_subset_model(
     return create_model(name, **fields)  # type: ignore
 
 
-def get_filtered_args(inferred_model: Type[BaseModel], func: Callable) -> dict:
+def get_filtered_args(
+    inferred_model: Type[BaseModel],
+    func: Callable,
+) -> dict:
     """Get the arguments from a function's signature."""
     schema = inferred_model.schema()["properties"]
     valid_keys = signature(func).parameters
     return {k: schema[k] for k in valid_keys}
 
 
-def create_schema_from_function(model_name: str, func: Callable) -> Type[BaseModel]:
+def create_schema_from_function(
+    model_name: str,
+    func: Callable,
+) -> Type[BaseModel]:
     """Create a pydantic schema from a function's signature."""
     inferred_model = validate_arguments(func).model  # type: ignore
     # Pydantic adds placeholder virtual fields we need to strip
@@ -102,12 +99,23 @@ class BaseTool(ABC, BaseModel, metaclass=ToolMetaclass):
     """Interface LangChain tools must implement."""
 
     name: str
+    """The unique name of the tool that clearly communicates its purpose."""
     description: str
+    """Used to tell the model how/when/why to use the tool.
+    
+    You can provide few-shot examples as a part of the description.
+    """
     args_schema: Optional[Type[BaseModel]] = None
     """Pydantic model class to validate and parse the tool's input arguments."""
     return_direct: bool = False
+    """Whether to return the tool's output directly. Setting this to True means
+    
+    that after the tool is called, the AgentExecutor will stop looping.
+    """
     verbose: bool = False
+    """Whether to log the tool's progress."""
     callback_manager: BaseCallbackManager = Field(default_factory=get_callback_manager)
+    """Callback manager for this tool."""
 
     class Config:
         """Configuration for this pydantic object."""
@@ -160,6 +168,14 @@ class BaseTool(ABC, BaseModel, metaclass=ToolMetaclass):
     async def _arun(self, *args: Any, **kwargs: Any) -> Any:
         """Use the tool asynchronously."""
 
+    def _to_args_and_kwargs(self, tool_input: Union[str, Dict]) -> Tuple[Tuple, Dict]:
+        # For backwards compatibility, if run_input is a string,
+        # pass as a positional argument.
+        if isinstance(tool_input, str):
+            return (tool_input,), {}
+        else:
+            return (), tool_input
+
     def run(
         self,
         tool_input: Union[str, Dict],
@@ -182,7 +198,7 @@ class BaseTool(ABC, BaseModel, metaclass=ToolMetaclass):
             **kwargs,
         )
         try:
-            tool_args, tool_kwargs = _to_args_and_kwargs(tool_input)
+            tool_args, tool_kwargs = self._to_args_and_kwargs(tool_input)
             observation = self._run(*tool_args, **tool_kwargs)
         except (Exception, KeyboardInterrupt) as e:
             self.callback_manager.on_tool_error(e, verbose=verbose_)
@@ -224,8 +240,8 @@ class BaseTool(ABC, BaseModel, metaclass=ToolMetaclass):
             )
         try:
             # We then call the tool on the tool input to get an observation
-            args, kwargs = _to_args_and_kwargs(tool_input)
-            observation = await self._arun(*args, **kwargs)
+            tool_args, tool_kwargs = self._to_args_and_kwargs(tool_input)
+            observation = await self._arun(*tool_args, **tool_kwargs)
         except (Exception, KeyboardInterrupt) as e:
             if self.callback_manager.is_async:
                 await self.callback_manager.on_tool_error(e, verbose=verbose_)
@@ -249,3 +265,62 @@ class BaseTool(ABC, BaseModel, metaclass=ToolMetaclass):
     def __call__(self, tool_input: Union[str, dict]) -> Any:
         """Make tool callable."""
         return self.run(tool_input)
+
+
+class StructuredTool(BaseTool):
+    """Tool that can operate on any number of inputs."""
+
+    description: str = ""
+    args_schema: Type[BaseModel] = Field(..., description="The tool schema.")
+    """The input arguments' schema."""
+    func: Callable[..., str]
+    """The function to run when the tool is called."""
+    coroutine: Optional[Callable[..., Awaitable[str]]] = None
+    """The asynchronous version of the function."""
+
+    @property
+    def args(self) -> dict:
+        """The tool's input arguments."""
+        return self.args_schema.schema()["properties"]
+
+    def _run(self, *args: Any, **kwargs: Any) -> Any:
+        """Use the tool."""
+        return self.func(*args, **kwargs)
+
+    async def _arun(self, *args: Any, **kwargs: Any) -> Any:
+        """Use the tool asynchronously."""
+        if self.coroutine:
+            return await self.coroutine(*args, **kwargs)
+        raise NotImplementedError("Tool does not support async")
+
+    @classmethod
+    def from_function(
+        cls,
+        func: Callable,
+        name: Optional[str] = None,
+        description: Optional[str] = None,
+        return_direct: bool = False,
+        args_schema: Optional[Type[BaseModel]] = None,
+        infer_schema: bool = True,
+        **kwargs: Any,
+    ) -> StructuredTool:
+        name = name or func.__name__
+        description = description or func.__doc__
+        assert (
+            description is not None
+        ), "Function must have a docstring if description not provided."
+
+        # Description example:
+        # search_api(query: str) - Searches the API for the query.
+        description = f"{name}{signature(func)} - {description.strip()}"
+        _args_schema = args_schema
+        if _args_schema is None and infer_schema:
+            _args_schema = create_schema_from_function(f"{name}Schema", func)
+        return cls(
+            name=name,
+            func=func,
+            args_schema=_args_schema,
+            description=description,
+            return_direct=return_direct,
+            **kwargs,
+        )

tests/unit_tests/agents/test_tools.py

@@ -1,7 +1,7 @@
 """Test tool utils."""
 from datetime import datetime
 from functools import partial
-from typing import Optional, Type, Union
+from typing import Any, Optional, Type, Union
 from unittest.mock import MagicMock
 
 import pydantic
@@ -16,7 +16,7 @@ from langchain.agents.mrkl.base import ZeroShotAgent
 from langchain.agents.react.base import ReActDocstoreAgent, ReActTextWorldAgent
 from langchain.agents.self_ask_with_search.base import SelfAskWithSearchAgent
 from langchain.agents.tools import Tool, tool
-from langchain.tools.base import BaseTool, SchemaAnnotationError
+from langchain.tools.base import BaseTool, SchemaAnnotationError, StructuredTool
 
 
 def test_unnamed_decorator() -> None:
@@ -27,7 +27,7 @@ def test_unnamed_decorator() -> None:
         """Search the API for the query."""
         return "API result"
 
-    assert isinstance(search_api, Tool)
+    assert isinstance(search_api, BaseTool)
     assert search_api.name == "search_api"
     assert not search_api.return_direct
     assert search_api("test") == "API result"
@@ -145,7 +145,7 @@ def test_decorator_with_specified_schema() -> None:
         """Return the arguments directly."""
         return f"{arg1} {arg2} {arg3}"
 
-    assert isinstance(tool_func, Tool)
+    assert isinstance(tool_func, BaseTool)
     assert tool_func.args_schema == _MockSchema
 
 
@@ -159,7 +159,7 @@ def test_decorated_function_schema_equivalent() -> None:
         """Return the arguments directly."""
         return f"{arg1} {arg2} {arg3}"
 
-    assert isinstance(structured_tool_input, Tool)
+    assert isinstance(structured_tool_input, BaseTool)
     assert structured_tool_input.args_schema is not None
     assert (
         structured_tool_input.args_schema.schema()["properties"]
@@ -171,14 +171,14 @@ def test_decorated_function_schema_equivalent() -> None:
 def test_structured_args_decorator_no_infer_schema() -> None:
     """Test functionality with structured arguments parsed as a decorator."""
 
-    @tool(infer_schema=False)
+    @tool
     def structured_tool_input(
         arg1: int, arg2: Union[float, datetime], opt_arg: Optional[dict] = None
     ) -> str:
         """Return the arguments directly."""
         return f"{arg1}, {arg2}, {opt_arg}"
 
-    assert isinstance(structured_tool_input, Tool)
+    assert isinstance(structured_tool_input, BaseTool)
     assert structured_tool_input.name == "structured_tool_input"
     args = {"arg1": 1, "arg2": 0.001, "opt_arg": {"foo": "bar"}}
     expected_result = "1, 0.001, {'foo': 'bar'}"
@@ -193,8 +193,9 @@ def test_structured_single_str_decorator_no_infer_schema() -> None:
         """Return the arguments directly."""
         return f"{tool_input}"
 
-    assert isinstance(unstructured_tool_input, Tool)
+    assert isinstance(unstructured_tool_input, BaseTool)
     assert unstructured_tool_input.args_schema is None
+    assert unstructured_tool_input.run("foo") == "foo"
 
 
 def test_base_tool_inheritance_base_schema() -> None:
@@ -225,18 +226,18 @@ def test_tool_lambda_args_schema() -> None:
         func=lambda tool_input: tool_input,
     )
     assert tool.args_schema is None
-    expected_args = {"tool_input": {"title": "Tool Input"}}
+    expected_args = {"tool_input": {"type": "string"}}
     assert tool.args == expected_args
 
 
-def test_tool_lambda_multi_args_schema() -> None:
+def test_structured_tool_lambda_multi_args_schema() -> None:
     """Test args schema inference when the tool argument is a lambda function."""
-    tool = Tool(
+    tool = StructuredTool.from_function(
         name="tool",
         description="A tool",
         func=lambda tool_input, other_arg: f"{tool_input}{other_arg}",  # type: ignore
     )
-    assert tool.args_schema is None
+    assert tool.args_schema is not None
     expected_args = {
         "tool_input": {"title": "Tool Input"},
         "other_arg": {"title": "Other Arg"},
@@ -268,7 +269,7 @@ def test_empty_args_decorator() -> None:
         """Return a constant."""
         return "the empty result"
 
-    assert isinstance(empty_tool_input, Tool)
+    assert isinstance(empty_tool_input, BaseTool)
     assert empty_tool_input.name == "empty_tool_input"
     assert empty_tool_input.args == {}
     assert empty_tool_input.run({}) == "the empty result"
@@ -282,7 +283,7 @@ def test_named_tool_decorator() -> None:
         """Search the API for the query."""
         return "API result"
 
-    assert isinstance(search_api, Tool)
+    assert isinstance(search_api, BaseTool)
     assert search_api.name == "search"
     assert not search_api.return_direct
 
@@ -295,7 +296,7 @@ def test_named_tool_decorator_return_direct() -> None:
         """Search the API for the query."""
         return "API result"
 
-    assert isinstance(search_api, Tool)
+    assert isinstance(search_api, BaseTool)
     assert search_api.name == "search"
     assert search_api.return_direct
 
@@ -308,7 +309,7 @@ def test_unnamed_tool_decorator_return_direct() -> None:
         """Search the API for the query."""
         return "API result"
 
-    assert isinstance(search_api, Tool)
+    assert isinstance(search_api, BaseTool)
     assert search_api.name == "search_api"
     assert search_api.return_direct
 
@@ -325,7 +326,7 @@ def test_tool_with_kwargs() -> None:
         """Search the API for the query."""
         return f"arg_0={arg_0}, arg_1={arg_1}, ping={ping}"
 
-    assert isinstance(search_api, Tool)
+    assert isinstance(search_api, BaseTool)
     result = search_api.run(
         tool_input={
             "arg_0": "foo",
@@ -423,3 +424,23 @@ def test_single_input_agent_raises_error_on_structured_tool(
         f" multi-input tool {the_tool.name}.",
     ):
         agent_cls.from_llm_and_tools(MagicMock(), [the_tool])  # type: ignore
+
+
+def test_tool_no_args_specified_assumes_str() -> None:
+    """Older tools could assume *args and **kwargs were passed in."""
+
+    def ambiguous_function(*args: Any, **kwargs: Any) -> str:
+        """An ambiguously defined function."""
+        return args[0]
+
+    some_tool = Tool(
+        name="chain_run",
+        description="Run the chain",
+        func=ambiguous_function,
+    )
+    expected_args = {"tool_input": {"type": "string"}}
+    assert some_tool.args == expected_args
+    assert some_tool.run("foobar") == "foobar"
+    assert some_tool.run({"tool_input": "foobar"}) == "foobar"
+    with pytest.raises(ValueError, match="Too many arguments to single-input tool"):
+        some_tool.run({"tool_input": "foobar", "other_input": "bar"})