Use is to compare NotImplemented

IPython/core/display.py

@@ -117,7 +117,7 b' def display(*objs, **kwargs):'
 
         # If _ipython_display_ is defined, use that to display this object.  If
         # it returns NotImplemented, use the _repr_ logic (default).
-        if not hasattr(obj, '_ipython_display_') or obj._ipython_display_(**kwargs) == NotImplemented:
+        if not hasattr(obj, '_ipython_display_') or obj._ipython_display_(**kwargs) is NotImplemented:
             if raw:
                 publish_display_data('display', obj, metadata)
             else:            

IPython/core/displayhook.py

@@ -243,7 +243,7 b' class DisplayHook(Configurable):'
         if result is not None and not self.quiet():
             # If _ipython_display_ is defined, use that to display this object.  If
             # it returns NotImplemented, use the _repr_ logic (default).
-            if not hasattr(result, '_ipython_display_') or result._ipython_display_() == NotImplemented:
+            if not hasattr(result, '_ipython_display_') or result._ipython_display_() is NotImplemented:
                 self.start_displayhook()
                 self.write_output_prompt()
                 format_dict, md_dict = self.compute_format_data(result)