second window in tkinter is not returning value

Question

I am trying to build a login window and after logging in, a second window with a list of options appears, the user should select a number and submit it in the second window. The login form works well, but the problem is that I am not able to extract the entered value from second window to put it in the function Admin() that is responsible for printing. I hope I am clear, if not I will answer any comments, thank you.

from tkinter import *
#User experience

def Admin():
    global selection
   
    value = selection.get()
    
    print("hi",selection.get())
    if value == '1':
        print("1")
    elif value == '2':
        print("2")
    elif value == '3':
        print("3")
    elif value == '4':
        print("4")
    elif value == '5':
        print("5")
    elif value == '6':
        print("6")
    elif value == '7':
        print("7")
        

import time
incorrect = 0
def login():
    
    #skipping the if username and password matches
    AdminF()
         
#defining loginform function
def Loginform():
        global login_screen
        login_screen = Tk()
        #Setting title of screen
        login_screen.title("Login Form")
        #setting height and width of screen
        login_screen.geometry("300x250")
        #declaring variable
        

          
        global  message
        global username
        global password
        
        username = StringVar()
        password = StringVar()
        message=StringVar()
        #Creating layout of login form
        Label(login_screen,width="300", text="Please enter details below", bg="orange",fg="white").pack()
        #Username Label
        Label(login_screen, text="Username * ").place(x=20,y=40)
        #Username textbox
    
        Entry(login_screen, textvariable=username).place(x=90,y=42)
        #Password Label
        Label(login_screen, text="Password * ").place(x=20,y=80)
        #Password textbox
        Entry(login_screen, textvariable=password ,show="*").place(x=90,y=82)
        #Label for displaying login status[success/failed]
       
        #Login button
        Button(login_screen, text="Login", width=10, height=1, bg="orange",command=login).place(x=105,y=130)
        Label(login_screen, text="" ,textvariable=message).place(x=95,y=100)
        login_screen.mainloop()
        
        
class AdminF:
    

    def __init__(self):
        global selection
        selection = StringVar()
        
        
        
        display = Tk()
        display.title("ADMIN")
        display.geometry("300x250")
        label = Label(display,width="300", text ="Welcome Admin", bg="orange",fg="white")
        label.pack()

        label = Label(display,width="300", text ="Please Select a Number", bg="white",fg="black")
        label.pack()
      
        label = Label(display,width="300", text ="\n1.print 1\n\
2.print 2 \n\
3.print 3\n\
4.print 4 \n\
5.print 5\n\
6.print 6 \n\
7.print 7 ", bg="orange",fg="white")
      
        label.pack()
        
        # Label(self, text="Selection: ").place(x=20,y=180)
        Entry(display, textvariable=selection).place(x=20,y=180, width = "260")
        #selection = entry.get()
        
        Button(display, text="submit", width=10, height=1, bg="orange", command = Admin).place(x=105,y=210)
        print("\n",selection.get())
        display.mainloop
        
        
Loginform()

Answer 1

Another way of expressing Don't use two instances of Tk, use Toplevel instead. – by Thingamabobs is stating:

Change the way of creating a second window from

display = Tk()

to

display = Toplevel(login_screen)

and you will get the value from the second window.

With

display = Toplevel(login_screen)
display.grab_set()

you can in addition also prevent interactions with the login_screen window and this way also trouble caused by creating multiple ADMIN windows from the login which all react to the submit button, but only one delivers the right user input value.

In the picture above clicking the right submit button will give the value 4 and not as eventually expected 7 .

Maybe someone with deeper insight into tkinter can point out in the comments how it comes that the Button press event is properly processed in the additional created windows but changes to the Entry content aren't ?

See https://www.pythontutorial.net/tkinter/tkinter-toplevel/ for more details about creating multiple windows in tkinter.

By the way: the

display.mainloop

command can be removed from your code in order to avoid confusion if trying to guess what it does and why it is necessary.