Make subunit init more robust

tests/test_subunit.py

@@ -140,7 +140,21 @@ def test_status_not_ok_ignored(
 
 
 def test_write_function_calls_connection_put(
-    connection, initialized_dummysubunit: SubunitBase, update_callback
+    connection, initialized_dummysubunit: DummySubunit, update_callback
 ):
     initialized_dummysubunit.dummy_function = 123
     connection.put.assert_called_with("UAW", "DUMMY_FUNCTION", "123")
+
+def test_unreadable_attributes_ignored(connection):
+    '''
+    This test is specifically to check handling of unreadable attributes
+    as found with issue https://github.com/mvdwetering/yamaha_ynca/issues/315
+    '''
+
+    class descriptor:
+        def __get__(self, instance, owner):
+            raise AttributeError("unreadable attribute")
+
+    DummySubunit.__provides__ = descriptor()
+    DummySubunit(connection)
+

ynca/subunit.py

@@ -56,7 +56,7 @@ def __init__(self, connection: YncaConnection) -> None:
         # otherwise the YncaFunction descriptors get/set functions would trigger.
         # Sort the list to have a deterministic/understandable order for easier testing
         for attribute_name in sorted(dir(self.__class__)):
-            attribute = getattr(self.__class__, attribute_name)
+            attribute = getattr(self.__class__, attribute_name, None)
             if isinstance(attribute, FunctionMixinBase):
                 self.function_handlers[attribute.name] = YncaFunctionHandler(attribute)