[FIX] Table: from_file/from_url remove type conversion

Orange/data/table.py

@@ -1077,11 +1077,6 @@ def from_file(cls, filename, sheet=None):
         reader.select_sheet(sheet)
         data = reader.read()
 
-        # Readers return plain table. Make sure to cast it to appropriate
-        # (subclass) type
-        if cls != data.__class__:
-            data = cls(data)
-
         # no need to call _init_ids as fuctions from .io already
         # construct a table with .ids
 
@@ -1093,8 +1088,6 @@ def from_url(cls, url):
         from Orange.data.io import UrlReader
         reader = UrlReader(url)
         data = reader.read()
-        if cls != data.__class__:
-            data = cls(data)
         return data
 
     # Helper function for __setitem__:

Orange/data/tests/test_table.py

@@ -385,6 +385,16 @@ def test_unpickled_owns_data(self):
         with unpickled.unlocked():
             unpickled.X[0, 0] = 42
 
+    @staticmethod
+    def test_unlock_table_derived():
+        # pylint: disable=abstract-method
+        class ExtendedTable(Table):
+            pass
+
+        t = ExtendedTable.from_file("iris")
+        with t.unlocked():
+            pass
+
 
 class TestTableFilters(unittest.TestCase):
     def setUp(self):

Orange/tests/test_naive_bayes.py

@@ -18,7 +18,10 @@
 
 
 class NotATable(Table):  # pylint: disable=too-many-ancestors,abstract-method
-    pass
+    @classmethod
+    def from_file(cls, *args, **kwargs):
+        table = super().from_file(*args, **kwargs)
+        return cls(table)
 
 
 class TestNaiveBayesLearner(unittest.TestCase):

Orange/tests/test_table.py

@@ -2163,19 +2163,6 @@ def test_value_assignment(self):
                     self.table[i, j] = new_value
                     self.assertEqual(self.table[i, j], new_value)
 
-    def test_subclasses(self):
-        from pathlib import Path
-
-        class _ExtendedTable(data.Table):
-            pass
-
-        data_file = _ExtendedTable('iris')
-        data_url = _ExtendedTable.from_url(
-            Path(os.path.dirname(__file__), 'datasets/test1.tab').as_uri())
-
-        self.assertIsInstance(data_file, _ExtendedTable)
-        self.assertIsInstance(data_url, _ExtendedTable)
-
 
 class TestTableStats(TableTests):
     def test_get_nan_frequency(self):