improve Py2/3 compat

Change-Id: I1dfdcb88a492401851d5157c734cd708496bf004
Reviewed-on: https://forge.frm2.tum.de/review/17734
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>

test/test_datatypes.py

@@ -107,9 +107,9 @@ def test_EnumType():
     with pytest.raises(TypeError):
         dt.validate([19, 'X'])
 
-    assert dt.validate('a') == 'a'
-    assert dt.validate('stuff') == 'stuff'
-    assert dt.validate(1) == 'stuff'
+    assert dt.validate('a') == 3
+    assert dt.validate('stuff') == 1
+    assert dt.validate(1) == 1
     with pytest.raises(ValueError):
         dt.validate(2)