Tkinter displaying data from database to new window

You could use normal way - import list - and later execute list.list() . This way you should have better control on windows.

But it needs to use Toplevel to create second window.

Minimal working example.

main.py

import tkinter as tk  # PEP8: `import *` is not preferredimport list as ls     # `list` is use to create list - don't use this name# --- functions ---def on_click():    # run method `list()` from file `list`    ls.list()# --- main ---root = tk.Tk()button = tk.Button(root, text='Second', command=on_click)button.pack()root.mainloop()

list.py

import tkinter as tk  # PEP8: `import *` is not preferreddef list():    second = tk.Toplevel()  # create inside function    dataLabel = tk.Label(second, text="Hello World")    dataLabel.grid(row=0, column=0)

BTW: In your version you probably forgot to execute list()

EDIT:

Version which check if window is not open already (main.py is the same)

list.py

import tkinter as tk  # PEP8: `import *` is not preferredsecond = None  # to control if window is opendef on_close():    global second        second.destroy()    second = None  # to control if window is open    def list():    global second        if second: # if second is not None:        print('Window already open')    else:        second = tk.Toplevel()        dataLabel = tk.Label(second, text="Hello World")        dataLabel.grid(row=0, column=0)        button = tk.Button(second, text='Close', command=on_close)        button.grid(row=1, column=0)