How to get a volume and a model object from in the scene management node?

This is the case, I loaded a volume and exported a model object, if only one, how to get these two objects in the scene management node! how is implemented in python code?Thanks!

You can get first instance of a certain MRML node class by calling slicer.mrmlScene.GetFirstNodeByClass("vtkMRMLVolumeNode"). However, you should not need this. If input comes from user then you ask the user to make a selection on the GUI. If you process data then you can always set/get the input and output nodes, so you don’t need blind lookup either.