How To Let Your Main Window Appear after succesful login in Tkinter(PYTHON 3.6

Question

This is ui which comes with default user name and password but after successful login the main UI needs to appear

Challenge

1. when you correctly input the

Answer 1

The below code can be used for the desired effect and is commented to show what is happening each step of the way:

from tkinter import * #Imports Tkinter
import sys #Imports sys, used to end the program later

root=Tk() #Declares root as the tkinter main window
top = Toplevel() #Creates the toplevel window

entry1 = Entry(top) #Username entry
entry2 = Entry(top) #Password entry
button1 = Button(top, text="Login", command=lambda:command1()) #Login button
button2 = Button(top, text="Cancel", command=lambda:command2()) #Cancel button
label1 = Label(root, text="This is your main window and you can input anything you want here")

def command1():
    if entry1.get() == "user" and entry2.get() == "password": #Checks whether username and password are correct
        root.deiconify() #Unhides the root window
        top.destroy() #Removes the toplevel window

def command2():
    top.destroy() #Removes the toplevel window
    root.destroy() #Removes the hidden root window
    sys.exit() #Ends the script


entry1.pack() #These pack the elements, this includes the items for the main window
entry2.pack()
button1.pack()
button2.pack()
label1.pack()

root.withdraw() #This hides the main window, it's still present it just can't be seen or interacted with
root.mainloop() #Starts the event loop for the main window

This makes use of the Toplevel widget in order to create a window which asks for the users details and then directs them to the main window which you can setup as you please.

You are also still able to use the pop up messages you have used in your example and if required you can also change the size of the Toplevel widget.

Please be advised however that this is not a particularly secure way of managing passwords and logins. As such I would suggest that you look up the proper etiquette for handling sensitive information in programming.