Interclass variable reference - python-3.x

Question

This is an example of some code I'm using to generate a form of populated values that will update itself when a field is changed. I've been stuck for a few days reading and experimenting with calling a variable from one class inside a method of another class. The reason that I'm attempting it this way, is to make the code more modular and readable since I'll end up having roughly 30 sections. Also, as a rule, I don't usually use numbers when naming objects.
from tkinter import *
from tkinter import ttk
class Application(ttk.Frame):
def __init__(self, master=None):
ttk.Frame.__init__(self, master)
self.grid()
Frame1()
Frame2()
Frame3()
class Frame1(ttk.Frame):
def __init__(self, master=None):
ttk.Frame.__init__(self, master)
self.grid()
ttk.Label(self, text="Frame1").grid()
self.var1 = IntVar()
self.SetVar1()
ttk.Label(self, textvariable=self.var1).grid()
def SetVar1(self):
self.var1.set(2)
class Frame2(ttk.Frame):
def __init__(self, master=None):
ttk.Frame.__init__(self, master)
self.grid()
ttk.Label(self, text="Frame2").grid()
self.var2 = IntVar()
self.SetVar2()
ttk.Label(self, textvariable=self.var2).grid()
def SetVar2(self):
self.var2.set(3)
class Frame3(ttk.Frame):
def __init__(self, master=None):
ttk.Frame.__init__(self, master)
self.grid()
ttk.Label(self, text="Frame3").grid()
self.var3 = IntVar()
self.SetVar3()
ttk.Label(self, textvariable=self.var3).grid()
def SetVar3(self):
self.var3.set(Frame1.var1.get() + Frame2.var2.get())
app = Application()
app.master.title("Window")
app.mainloop()
Toward the bottom of the code the error occurs for
def SetVar3(self):
self.var3.set(Frame1.var1.get() + Frame2.var2.get())
and I cannot get past it. Apparently I cannot call var1 in this manner. It results in the following error.
AttributeError: type object 'Frame1' has no attribute 'var1'
When executed properly, the code should resemble:
Frame1
2
Frame2
3
Frame3
5
So, what am I missing?
(A moment ago there were comments below, but they've since disappeared which really helps discuss this topic. I'll pick this back up after some sleep. Maybe by then the comments below will have magically reappeared and I can respond to them in turn.
One comment mentioned creating new instances of Frame1 and Frame2 to call in Frame3, but it wouldn't help unless these new instances shared the values from the already initialized instances in Application. The other comment mentioned that I had errors in my code, but didn't elaborate.
While I responding to each comment, each disappeared and I was given a warning to edit my original post instead. Did I miss something about the point of comments?)

Answer 1

Frame1 and Frame2 are both classes, not instances. That's why you're getting an error in that line of code (var1 and var2 are instance variables, not class variables).
To make this work you'll need to pass a reference to your Frame1 and Frame2 instances (or perhaps, to those instances var1 and var2 variable) to Frame3.
Try changing Application to:
class Application(ttk.Frame):
def __init__(self, master=None):
ttk.Frame.__init__(self, master)
self.grid()
f1 = Frame1() # save frames to local variables, so we can reference them
f2 = Frame2()
f3 = Frame3(f1, f2) # pass previous frames as args!
Then make Frame3 use the parameters (here I just pass them on to SetVar3 directly from __init__, but you could save them as attributes on self instead, if you wanted):
class Frame3(ttk.Frame):
def __init__(self, f1, f2, master=None): # take other frames as parameters
ttk.Frame.__init__(self, master)
self.grid()
ttk.Label(self, text="Frame3").grid()
self.var3 = IntVar()
self.SetVar3(f1, f2) # pass frames on
ttk.Label(self, textvariable=self.var3).grid()
def SetVar3(self, f1, f2): # take frames as parameters here too
self.var3.set(f1.var1.get() + f2.var2.get()) # use the references
Obviously in real code the logic might need to be different. Think about what the logical relationships are between the frames, and let them pass (and perhaps save) references to each other as appropriate.