pass a variable between tkinter and toplevel windows

[janeik]

I would do it like this:

import tkinter as tk
import customtkinter as ctk


class OverlayWindow(tk.Toplevel):
    def __init__(self, overlay_file):
        self.overlay_file = overlay_file
        super().__init__()
        self.geometry("1000x1000")   
        self.resizable(False, False) 
        self.overrideredirect(True)
        tk.Button(self, text="Submit", command=self.loading).place(x=45,y=1140)

    def loadimg(self):
        """Set overlay image"""
        photo = tk.PhotoImage(file=self.overlay_file.get().strip())
        image_label = tk.Label(self, image=photo)
        image_label.photo = photo
        image_label.place(x=0, y=0)


class MainWindow(tk.Tk):
    def __init__(self):
        super().__init__()
        self.geometry("1920x1200+0+0")
        self.minsize(1920, 1200)
        self.resizable(False, False)
        self.overrideredirect(True)
        self.attributes('-topmost',True)

        self.overlay_file = tk.StringVar()
        ctk.CTkEntry(
            self,
            textvariable=self.overlay_file,
            width=360,
            font=("Ariel", 14, "bold"),
            placeholder_text="Sti til bilde 1 som skal behandles.(d:/bilde/abc.png)",
            justify=("left")).place(x=12,y=1010)

window = MainWindow()
top = OverlayWindow(window.overlay_file)

If there are several values that top needs to get from window, I pass window to top, and use that to reference the values.

class OverlayWindow(tk.Toplevel):
    def __init__(self, main_window):
        self.main_window = main_window
        super().__init__()
        self.geometry("1000x1000")   
        self.resizable(False, False) 
        self.overrideredirect(True)
        tk.Button(self, text="Submit", command=self.loading).place(x=45,y=1140)

    def loadimg(self):
        """Set overlay image"""
        photo = tk.PhotoImage(file=self.main_window.overlay.get().strip())
        image_label = tk.Label(self, image=photo)
        image_label.photo = photo
        image_label.place(x=0, y=0)

Another approach is to make a data model that is used by both windows. Think of it as a blackboard that both windows can read and write.

import tkinter as tk
import customtkinter as ctk


class ApplicationData():
    """I have all data shared between the main and overlay window."""
    def __init__(self):
        self.overlay_file = tk.StringVar()
        # additional shared vaiables go here


class OverlayWindow(tk.Toplevel):
    def __init__(self, data):
        self.data = data
        super().__init__()
        self.geometry("1000x1000")   
        self.resizable(False, False) 
        self.overrideredirect(True)
        tk.Button(self, text="Submit", command=self.loading).place(x=45,y=1140)

    def loadimg(self):
        """Set overlay image"""
        photo = tk.PhotoImage(file=self.data.overlay_file.get().strip())
        image_label = tk.Label(self, image=photo)
        image_label.photo = photo
        image_label.place(x=0, y=0)


class MainWindow(tk.Tk):
    def __init__(self, data):
        super().__init__()
        self.geometry("1920x1200+0+0")
        self.minsize(1920, 1200)
        self.resizable(False, False)
        self.overrideredirect(True)
        self.attributes('-topmost',True)

        ctk.CTkEntry(
            self,
            textvariable=self.data.overlay_file,
            width=360,
            font=("Ariel", 14, "bold"),
            placeholder_text="Sti til bilde 1 som skal behandles.(d:/bilde/abc.png)",
            justify=("left")).place(x=12,y=1010)


data = ApplicationData()
window = MainWindow(data)
top = OverlayWindow(data)

You should start studying Python classes. There is a reason that tkinter and customtkinter use classes. It is hard to write good looking GUI code without them.

Thanks for thee advices. I will probably change to oop affter Im finished without oop :)