Fix function_tool method detection

Author: adit24dhaya

src/agents/tool.py

@@ -1841,7 +1841,11 @@ def function_tool(
 
     def _is_instance_method_tool(the_func: ToolFunction[...]) -> bool:
         parameters = tuple(inspect.signature(the_func).parameters.values())
-        return bool(parameters) and parameters[0].name == "self"
+        if not parameters:
+            return False
+
+        parent_name = the_func.__qualname__.rsplit(".", 1)[0]
+        return "." in the_func.__qualname__ and not parent_name.endswith("<locals>")
 
     def _create_function_tool(
         the_func: ToolFunction[...],

tests/test_function_tool.py

@@ -180,6 +180,50 @@ def lookup(self, account_id: str) -> str:
     assert result == "acct:123"
 
 
+@pytest.mark.asyncio
+async def test_instance_method_function_tool_binds_non_self_receiver_name():
+    class AccountTools:
+        def __init__(self, prefix: str) -> None:
+            self.prefix = prefix
+
+        @function_tool
+        def lookup(this, account_id: str) -> str:
+            """Look up an account."""
+            return f"{this.prefix}:{account_id}"
+
+    tools = AccountTools("acct")
+    tool = tools.lookup
+
+    assert "this" not in tool.params_json_schema["properties"]
+    assert "account_id" in tool.params_json_schema["properties"]
+
+    result = await tool.on_invoke_tool(
+        ToolContext(None, tool_name=tool.name, tool_call_id="1", tool_arguments=""),
+        '{"account_id": "123"}',
+    )
+
+    assert result == "acct:123"
+
+
+@pytest.mark.asyncio
+async def test_function_tool_does_not_treat_self_named_argument_as_method():
+    def lookup(self: str, account_id: str) -> str:
+        """Look up an account."""
+        return f"{self}:{account_id}"
+
+    tool = function_tool(lookup)
+
+    assert "self" in tool.params_json_schema["properties"]
+    assert "account_id" in tool.params_json_schema["properties"]
+
+    result = await tool.on_invoke_tool(
+        ToolContext(None, tool_name=tool.name, tool_call_id="1", tool_arguments=""),
+        '{"self": "acct", "account_id": "123"}',
+    )
+
+    assert result == "acct:123"
+
+
 @pytest.mark.asyncio
 async def test_instance_method_function_tool_supports_context_after_self():
     class AccountTools: