[ENH] Domain: Add copy method

Orange/data/domain.py

@@ -444,6 +444,21 @@ def _compute_col_indices(self, col_idx):
     def checksum(self):
         return hash(self)
 
+    def copy(self):
+        """
+        Make a copy of the domain. New features are proxies of the old ones,
+        hence the new domain can be used anywhere the old domain was used.
+
+        Returns:
+            Domain: a copy of the domain.
+        """
+        return Domain(
+            attributes=[a.make_proxy() for a in self.attributes],
+            class_vars=[a.make_proxy() for a in self.class_vars],
+            metas=[a.make_proxy() for a in self.metas],
+            source=self,
+        )
+
     def __eq__(self, other):
         if not isinstance(other, Domain):
             return False

Orange/tests/test_domain.py

@@ -490,6 +490,18 @@ def test_domain_conversion_is_fast_enough(self):
 
         self.assertLessEqual(time() - start, 1)
 
+    def test_copy(self):
+        age.number_of_decimals = 5
+        attributes = (age, gender, income)
+
+        domain = Domain(attributes, [race], [ssn])
+
+        new_domain = domain.copy()
+        new_domain[age].number_of_decimals = 10
+
+        self.assertEqual(domain[age].number_of_decimals, 5)
+        self.assertEqual(new_domain[age].number_of_decimals, 10)
+
 
 class TestDomainFilter(unittest.TestCase):
     def setUp(self):