[fileio] use to-string in display method

Author: jgrewe

odml/fileio.py

@@ -14,5 +14,5 @@ def save(obj, filename, backend="xml"):
 
 
 def display(obj, backend="xml"):
-    # needs to be handled through the generic ODMLWriter
-    pass
+    writer = ODMLWriter(backend)
+    print(writer.to_string(obj))

test/test_fileio.py

@@ -36,6 +36,6 @@ def test_invalid_parser(self):
         with self.assertRaises(NotImplementedError):
             odml.save(doc, self.file + '_copy_html', 'html')
 
-        # odml.display not implemented
-        # with self.assertRaises(NotImplementedError):
-        #     odml.display(doc, 'html')
+        with self.assertRaises(NotImplementedError):
+            odml.display(doc, 'html')
+