[FIX] Variable: Fix Variable.copy for StringVariable and TimeVariable

Orange/data/variable.py

@@ -427,7 +427,7 @@ def __reduce__(self):
         return make_variable, (self.__class__, self._compute_value, self.name), self.__dict__
 
     def copy(self, compute_value):
-        var = Variable(self.name, compute_value)
+        var = type(self)(self.name, compute_value=compute_value)
         var.attributes = dict(self.attributes)
         return var
 
@@ -524,7 +524,7 @@ def repr_val(self, val):
     str_val = repr_val
 
     def copy(self, compute_value=None):
-        var = ContinuousVariable(self.name, self.number_of_decimals, compute_value)
+        var = type(self)(self.name, self.number_of_decimals, compute_value)
         var.attributes = dict(self.attributes)
         return var
 
@@ -905,6 +905,12 @@ def __init__(self, *args, **kwargs):
         self.have_date = 0
         self.have_time = 0
 
+    def copy(self, compute_value=None):
+        copy = super().copy(compute_value=compute_value)
+        copy.have_date = self.have_date
+        copy.have_time = self.have_time
+        return copy
+
     @staticmethod
     def _tzre_sub(s, _subtz=re.compile(r'([+-])(\d\d):(\d\d)$').sub):
         # Replace +ZZ:ZZ with ISO-compatible +ZZZZ, or strip +0000

Orange/tests/test_variable.py

@@ -58,6 +58,7 @@ def test_copy_copies_attributes(self):
         var.attributes["a"] = "b"
         var2 = var.copy(compute_value=None)
         self.assertIn("a", var2.attributes)
+        self.assertIsInstance(var2, type(var))
 
         var2.attributes["a"] = "c"
         # Attributes of original value should not change