Fix SetterAwareType if __slots__ is tuple.

src/robot/utils/setter.py

@@ -38,9 +38,10 @@ def __set__(self, instance, value):
 class SetterAwareType(type):
 
     def __new__(cls, name, bases, dct):
-        slots = dct.get('__slots__')
-        if slots is not None:
+        if '__slots__' in dct:
+            slots = list(dct['__slots__'])
             for item in dct.values():
                 if isinstance(item, setter):
                     slots.append(item.attr_name)
+            dct['__slots__'] = slots
         return type.__new__(cls, name, bases, dct)

utest/utils/test_setter.py

@@ -4,11 +4,7 @@
 from robot.utils import setter, SetterAwareType
 
 
-class BaseWithMeta(metaclass=SetterAwareType):
-    __slots__ = []
-
-
-class ExampleWithSlots(BaseWithMeta):
+class ExampleWithSlots(metaclass=SetterAwareType):
     __slots__ = []
 
     @setter
@@ -54,6 +50,22 @@ def setUp(self):
     def test_set_other_attr(self):
         assert_raises(AttributeError, setattr, self.item, 'other_attr', 1)
 
+    def test_slots_as_tuple(self):
+        class XY(metaclass=SetterAwareType):
+            __slots__ = ('x',)
+
+            def __init__(self, x, y):
+                self.x = x
+                self.y = y
+
+            @setter
+            def y(self, y):
+                return y.upper()
+
+        xy = XY('x', 'y')
+        assert_equal((xy.x, xy.y), ('x', 'Y'))
+        assert_raises(AttributeError, setattr, xy, 'z', 'z')
+
 
 if __name__ == '__main__':
     unittest.main()