How to embed a matplotlib annotation action into a function?

Question

With matplotlib you can have interaction with a plotted image for instance for annotation. You then get after the interaction some data that you usually like to save. I would like to incorporate that all in a function, but I don't know how to do this. The spectral module illustrates my problem, but I encountered this before.

Here is some code:

import spectral  as spy

class Annotator:
    def __init__(self, filename):
        self.filename = filename
        self.classes = list(zip(range(5), ['unknown','background','tape','healthy','infected']))
    def img(self): 
        img=spy.open_image(self.filename)
        return img
    def viewer(self):
        img = self.img()
        print(self.classes)
        viewer = spy.imshow(img)
        annotation = viewer.classes
        return annotation

If I call an Annotator An=Annotator(some data file), and then call the viewer and annotate

results = An.viewer

then python parses right away to the end, and gives as results an empty none type object. I would like the code to break, such that I can get the annotation and save it in the same function call.

So my question is, how do I do that?