Quick fix

responder/routes.py

@@ -79,6 +79,7 @@ class Route:
     def is_class_based(self):
         return hasattr(self.endpoint, "__class__")
 
+    @property
     def is_function(self):
         routed = hasattr(self.endpoint, "is_routed")
         code = hasattr(self.endpoint, "__code__")