Python • AttributeError: 'App' object has no attribute 'button' tkinter and gpiozero

Code:

import tkinter as tkfrom gpiozero import Button as btnbutton = btn(4)class App:    def __init__(self, root=None):        self.root = root        self.frame = tk.Frame(self.root)        self.frame.pack()        tk.Label(self.frame, text='Main page').pack()self.button.when_pressed = self.make_page_1        self.page_1 = Page_1(master=self.root, app=self)    def main_page(self):        print(4)        self.frame.pack()    def make_page_1(self):        print(1)        self.frame.pack_forget()        self.page_1.start_page()class Page_1:    def __init__(self, master=None, app=None):        self.master = master        self.app = app        self.frame = tk.Frame(self.master)        tk.Label(self.frame, text='Page 1').pack()        tk.Button(self.frame, text='Go back', command=self.go_back).pack() #botton    def start_page(self):        print(2)        self.frame.pack()    def go_back(self):        print(3)        self.frame.pack_forget()        self.app.main_page()if __name__ == '__main__':    root = tk.Tk()    app = App(root)    root.mainloop()