Updating TKinter frames with child classes

I’m currently making a GUI for a python program, and am using TKinter in an OOP fashion. I have a root class which creates a window and creates an array of all frames in the program, where each frame is a child class, and a method ‘show_frame’ which when called will update the window to show the frame passed as an argument. However I am having issues calling the show_frame method within methods of child classes, I was wondering if this is possible?

The root class:

from tkinter import *
from tkinter import ttk

class rootClass(Tk):
    def __init__(self): 
        
        Tk.__init__(self)
        
        window = Frame(self) 
        self.title("Application")
        window.pack(side="top", fill="both", expand=True) 
        window.grid_rowconfigure(0, weight = 1)
        window.grid_columnconfigure(0, weight = 1)
        self.frames = {} 

        pagesTuple = (firstPage, secondPage, thirdPage)
        for F in pagesTuple:
            frame = F(window, self)
            self.frames[F] = frame 
            frame.grid(row = 0, column = 0, sticky ="NSEW")

        self.show_frame(firstPage)

    def show_frame(self, cont):
        frame = self.frames[cont]
        frame.tkraise()

The first child class:

class firstPage(Frame):

    def newPageMethod(self, controller, newPage):
                print("newPageMethod executed")
                controller.show_frame(newPage)
    def __init__(self, parent, controller): 
        super().__init__(parent)
        
        titleLabel = Label(self, text ="firstPage")
        titleLabel.grid(row = 0, column = 1, padx = 10, pady = 10) 

        loginButton = Button(self, text ="go to second page", command = self.newPageMethod(controller, secondPage))
        loginButton.grid(row = 1, column = 1, padx = 10, pady = 10)

Second child class:

class secondPage(Frame):

    def newPageMethod(self, controller, newPage):
                print("newPageMethod executed")
                controller.show_frame(newPage)
    def __init__(self, parent, controller): 
        super().__init__(parent)
        
        titleLabel = Label(self, text ="secondPage")
        titleLabel.grid(row = 0, column = 1, padx = 10, pady = 10) 

        loginButton = Button(self, text ="go to third page", command = self.newPageMethod(controller, thirdPage))
        loginButton.grid(row = 1, column = 1, padx = 10, pady = 10)

And so on. The error being returned is:

    frame = self.frames[cont]

KeyError: <class '__main__.firstPage'>

>Solution :

The error comes from:

loginButton = Button(self, text ="go to second page", command = self.newPageMethod(controller, secondPage))

When creating the button, instead of passing self.newPageMethod as argument to Button you are calling the function.

Then the show_frame function is called and it tries to get the value from cont key before the key is even assigned:

        for F in pagesTuple:
            frame = F(window, self) # calls 'show_frame' before assigning the key
            self.frames[F] = frame # assigning the key
            frame.grid(row = 0, column = 0, sticky ="NSEW")

    def show_frame(self, cont):
        frame = self.frames[cont] # ---> error here
        frame.tkraise()

That can be fixed using the lambda function:

        loginButton = Button(self, text ="go to second page", command = lambda: self.newPageMethod(controller, secondPage))

And also here:

        loginButton = Button(self, text ="go to third page", command = lambda: self.newPageMethod(controller, thirdPage))

And I am guessing that it should also be fixed in your other classes as well.