Support kwargs in dspy Tool (#8102)

* support kwargs in dspy Tool

Co-authored-by: ButterflyAtHeart <[email protected]>

* improve comment

---------

Co-authored-by: ButterflyAtHeart <[email protected]>

Author: TomeHirata

dspy/primitives/tool.py

@@ -57,6 +57,7 @@ def foo(x: int, y: str = "hello"):
         self.args = args
         self.arg_types = arg_types
         self.arg_desc = arg_desc
+        self.has_kwargs = False
 
         self._parse_function(func, arg_desc)
 
@@ -129,6 +130,7 @@ def _parse_function(self, func: Callable, arg_desc: dict[str, str] = None):
         self.desc = self.desc or desc
         self.args = self.args or args
         self.arg_types = self.arg_types or arg_types
+        self.has_kwargs = any([param.kind == param.VAR_KEYWORD for param in sig.parameters.values()])
 
     def _parse_args(self, **kwargs):
         parsed_kwargs = {}
@@ -147,6 +149,9 @@ def _parse_args(self, **kwargs):
     def __call__(self, **kwargs):
         for k, v in kwargs.items():
             if k not in self.args:
+                if self.has_kwargs:
+                    # If the tool has kwargs, skip validation for unknown args
+                    continue
                 raise ValueError(f"Arg {k} is not in the tool's args.")
             try:
                 instance = v.model_dump() if hasattr(v, "model_dump") else v

tests/primitives/test_tool.py

@@ -193,3 +193,12 @@ def dummy_function(x: list[list[DummyModel]]):
 
     result = tool(**args)
     assert result == [[DummyModel(field1="hello", field2=123)]]
+
+
+def test_tool_call_kwarg():
+    def fn(x: int, **kwargs):
+        return kwargs
+    tool = Tool(fn)
+
+    assert tool(x=1, y=2, z=3) == {"y": 2, "z": 3}
+