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guis and data

The system tells the other widgets when

the model changes

The tkinter library code will keep a track of which widgets are using which
models and, whenever a model changes, tkinter will let the widgets know
about it. So if we select the Seattle, WA radio button, it will update
the model, and the other radio buttons that share the model will deselect
themselves.
Well, that‛s not my
value, so I'd better
deselect myself.

Hey, I‛m set
to “Seattle,
WA” now.

Seattle, WA

Not mine
either.
Deselect.

There’s a special name for the way this code works:

Model View Controller

The model is the data stored.

The view is just a fancy name for the widget.

And the controller is the code in tkinter that lets all of the views know
when the model has changed.

So much for the MVC theory. Time to fix the code.

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