To show this warning:
Modules-Developer Tools-Extension Wizard-Create Extension-Add Module
Open the module just created, switch to another module, then back to this module, you can see the warning:
/Applications/Slicer.app/Contents/bin/Python/slicer/util.py:2486: UserWarning: does not have observer
warn('does not have observer')
It comes from:
if self._parameterNode is not None:
self.removeObserver(self._parameterNode, vtk.vtkCommand.ModifiedEvent, self.updateGUIFromParameterNode)
This warning shows in Slicer 5.0.3, but not in the previous versions.
It’s an unrelated bug with the ScriptedModule template. Observers are already removed when exiting the module, however they are “removed” a second time when the user enters the module and setParameterNode() is called.
The fix that @Sunderlandkyl implemented in the module template had to be done in the TotalSegmentator module, too. It would be great if you could edit the file accordingly and if everything works well then send a pull request with the suggested changes.