Allow react.Tool to wrap methods (#1856)

The big reason for this is to pass parameters out-of-band, e.g. a
user_id to ensure the LLM doesn't get the wrong data.

The unit test includes a usage, you can't use it as a decorator this
way, but it works.

The alternative, of course, is to have a very long function and have all
the tools be nested functions. It works, but can lead to some very long
functions. I prefer long classes over long functions.

dspy/predict/react.py

@@ -9,7 +9,7 @@
 
 class Tool:
     def __init__(self, func: Callable, name: str = None, desc: str = None, args: dict[str, Any] = None):
-        annotations_func = func if inspect.isfunction(func) else func.__call__
+        annotations_func = func if inspect.isfunction(func) or inspect.ismethod(func) else func.__call__
         self.func = func
         self.name = name or getattr(func, '__name__', type(func).__name__)
         self.desc = desc or getattr(func, '__doc__', None) or getattr(annotations_func, '__doc__', "")

tests/predict/test_react.py

@@ -2,6 +2,7 @@
 
 import dspy
 from dspy.utils.dummies import DummyLM, dummy_rm
+from dspy.predict import react
 
 
 # def test_example_no_tools():
@@ -121,4 +122,28 @@
 #     react = dspy.ReAct(ExampleSignature)
 
 #     assert react.react[0].signature.instructions is not None
-#     assert react.react[0].signature.instructions.startswith("You are going to generate output based on input.")
+#     assert react.react[0].signature.instructions.startswith("You are going to generate output based on input.")
+
+def test_tool_from_function():
+    def foo(a: int, b: int) -> int:
+        """Add two numbers."""
+        return a + b
+
+    tool = react.Tool(foo)
+    assert tool.name == "foo"
+    assert tool.desc == "Add two numbers."
+    assert tool.args == {"a": "int", "b": "int"}
+
+def test_tool_from_class():
+    class Foo:
+        def __init__(self, user_id: str):
+            self.user_id = user_id
+
+        def foo(self, a: int, b: int) -> int:
+            """Add two numbers."""
+            return a + b
+
+    tool = react.Tool(Foo("123").foo)
+    assert tool.name == "foo"
+    assert tool.desc == "Add two numbers."
+    assert tool.args == {"a": "int", "b": "int"}