We have that handle persistence note somewhere else as well. Do we need to find other places for it?

Do you mean add a note other places where we need to keep objects alive?

One coud do that. There's at least the following examples with similar patterns in the Event handling examples:

• https://matplotlib.org/devdocs/gallery/event_handling/trifinder_event_demo.html
• https://matplotlib.org/devdocs/gallery/event_handling/viewlims.html
• https://matplotlib.org/devdocs/gallery/event_handling/zoom_window.html
• https://matplotlib.org/devdocs/gallery/event_handling/poly_editor.html
• https://matplotlib.org/devdocs/gallery/event_handling/pong_sgskip.html
• https://matplotlib.org/devdocs/gallery/event_handling/resample.html
• https://matplotlib.org/devdocs/gallery/event_handling/lasso_demo.html
• https://matplotlib.org/devdocs/gallery/event_handling/looking_glass.html
• https://matplotlib.org/devdocs/gallery/event_handling/path_editor.html
• https://matplotlib.org/devdocs/gallery/event_handling/cursor_demo.html
• https://matplotlib.org/devdocs/gallery/event_handling/data_browser.html

plus probably additional ones in Widgets.

However, this is beyond what I'm willing to do right now. We can open an issue for it.

On a general note, I'm not very convinced of this pattern to create a complex object and bind it's methods to a figure. IMHO it would make more sense for the ImageTracker to create and own the figure.

On a general note, I'm not very convinced of this pattern to create a complex object and bind it's methods to a figure. IMHO it would make more sense for the ImageTracker to create and own the figure.

The pattern of an independent object that knows about the Figure and provides some interaction does match how I have frequently used this sort of thing. I've either hand a couple of these that I turn on and off or have been embedding in a larger GUI where if each one tried to make its own Figure object it would have caused some trouble for me.

I'm also wary of going to pure-functions because in my experience I have wanted to pull state off of these classes.