Tkinter opens second GUI first

Question

I'm trying to build a login screen for practice and I'm having trouble with it. The general idea is that pressing the Login button closes the current window and opens another in a separate file. However, when I run the main file it opens the GUI window created in the second file. I'm not sure what would be causing it to do this.

import tkinter as tk
import loginEntry

HEIGHT = 200
WIDTH = 500


def login_function():
    root.destroy()
    loginEntry.NewScreen()


def register_function():
    print("Register!")


root = tk.Tk()

root.title("Login Screen")
root.resizable(False, False)

canvas = tk.Canvas(root, height = HEIGHT, width = WIDTH)
canvas.pack()

frame = tk.Frame(root, bg='grey')
frame.place(relx=0.1, rely=0.25, relwidth=0.8, relheight=0.5)

login = tk.Button(frame, text="Login", command=login_function)
login.place(relx=0.05, rely=0.25, relwidth=0.425, relheight=0.5,)

register = tk.Button(frame, text="Register", command=register_function)
register.place(relx=0.525, rely=0.25, relwidth=0.425, relheight=0.5,)

introduction = tk.Label(root, text="Hello and welcome to DogNet, please login below.", font='bold 12')
introduction.place(relx=0.5, anchor='center', rely=0.1)

root.mainloop()

and then the second file

import tkinter as tk

def NewScreen():
    root = tk.Tk()

    canvas = tk.Canvas(root, bg='black')
    canvas.pack()

    root.mainloop()

NewScreen()

Read [Why are multiple instances of Tk discouraged?](https://stackoverflow.com/questions/48045401/why-are-multiple-instances-of-tk-discouraged) — stovfl, Oct 03 '19 at 13:42

score 1 · Answer 1 · answered Oct 03 '19 at 13:08

1

This is because, in your second file, you are calling the definition when it is imported.

import tkinter as tk

def NewScreen():
    root = tk.Tk()

    canvas = tk.Canvas(root, bg='black')
    canvas.pack()

    root.mainloop()

NewScreen() #< here you call the definition

This means that the series of events that happen in your program are as follows.

First file starts
Second file is imported
Definition "NewScreen" is called
tkinter mainloop starts which puts your program into a loop and stops the program from going on to any new lines until the loop is closed

answered Oct 03 '19 at 13:08

Ethan Field

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That makes sense! I'm not sure how to stop it from doing this though? Will it always run NewProgram when it's imported? – Bramblethorns Oct 03 '19 at 13:11
It is running NewProgram because you tell it to on the last line of your second file. – Ethan Field Oct 03 '19 at 13:21
@Bramblethorns We all do it sometimes! – Ethan Field Oct 03 '19 at 13:39

Tkinter opens second GUI first

1 Answers1