Update app.py

app.py

@@ -26,7 +26,8 @@ def concat_tool(arg1:str, arg2:str)-> str: #it's import to specify the return ty
         arg1: the first argument given by user
         arg2: the second argument given by user
     """
-    return "arg1 + arg2"
+    result = "arg1 + arg2"
+    return result
 
 @tool
 def get_current_time_in_timezone(timezone: str) -> str: