Implement Orange.widget.utils.signals.lazy_table_transform

Orange/widgets/utils/signals.py

@@ -1,8 +1,12 @@
+from typing import Optional
+
 from orangewidget.utils.signals import (
     Input, Output, Single, Multiple, Default, NonDefault, Explicit, Dynamic,
-    InputSignal, OutputSignal, WidgetSignalsMixin
+    InputSignal, OutputSignal, WidgetSignalsMixin, LazyValue
 )
 
+from Orange.data import Table, Domain
+
 __all__ = [
     "Input", "Output", "InputSignal", "OutputSignal",
     "Single", "Multiple", "Default", "NonDefault", "Explicit", "Dynamic",
@@ -12,3 +16,11 @@
 
 class AttributeList(list):
     """Signal type for lists of attributes (variables)"""
+
+
+def lazy_table_transform(domain: Domain,
+                         data: Optional[Table]) -> LazyValue[Table]:
+    if data is None:
+        return None
+    return LazyValue[Table](lambda: data.transform(domain),
+                            domain=domain, length=len(data))

Orange/widgets/utils/tests/test_signals.py

@@ -0,0 +1,27 @@
+import unittest
+from unittest.mock import Mock
+
+from Orange.widgets.utils.signals import lazy_table_transform
+
+
+class TestSignals(unittest.TestCase):
+    def test_lazy_table_transform(self):
+        data = Mock()
+        data.__len__ = lambda _: 42
+        data.transform = Mock()
+
+        domain = Mock()
+
+        lazy_trans = lazy_table_transform(domain, data)
+
+        data.transform.assert_not_called()
+        self.assertEqual(lazy_trans.length, 42)
+        self.assertIs(lazy_trans.domain, domain)
+        self.assertFalse(lazy_trans.is_cached)
+
+        self.assertIs(lazy_trans.get_value(), data.transform.return_value)
+        data.transform.assert_called_once()
+
+
+if __name__ == '__main__':
+    unittest.main()