Re: don't understand namespaces...

Lawrence Hanser wrote:
Dear Pythoners,

I think I do not yet have a good understanding of namespaces. Here is
what I have in broad outline form:

------------------------------------
import Tkinter

Class App(Frame)
define two frames, buttons in one and Listbox in the other

Class App2(Frame)
define one frame with a Text widget in it

root = Tk()
app = App(root)
win2 = Toplevel(root)
app2 = App2(win2)
root.mainloop()
------------------------------------

My understanding of the above goes like this:
1) create a root window
2) instantiate a class that defines a Frame in the root window
3) create another Toplevel window
4) instantiate another class that defines a frame in the Toplevel window (win
What I cannot figure out is how to reference a widget in app2 from app...

I hope this is sort of clear.

Any assistance appreciated.

Thanks,

Larry

A couple of things about your message confused me greatly, but I think I can help anyway.

1) please don't call window classes "AppXX", since an App has a very different meaning in GUI parlance.
2) namespaces are very different than what you're asking, as they describe how symbols are searched when they're not directly accessible within the class or within a function.

Anyway, back to your real question: Since you're instantiating subclasses of Frame, you have control of the __init__() method. There already is a "parent" parameter, so save it as a instance attribute. That gets you upward references. And the caller gets a return value from the constructor, which is a downward reference.

If you pick a consistent naming, you can simply walk the objects with dot notation. I find it easiest if each class usually instantiates all its own children, and therefore saves instance attributes of each of them. If you followed that convention, then app2 could find app by using self.parent.parent.app

Another approach is to create one extra class object which holds references to everything needed. Then each child is passed a reference to that instance in its constructors. The problem with this is that everything gets a bit too tightly coupled.

Usually some combination works best.

DaveA
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