How to open a new window by the user pressing a button in a tkinter GUI?

Tkinter creates a default window (i.e., master or root window) for every application. In tkinter, we can create a popup window or child window by defining a Toplevel(master) constructor. This will allow the tkinter application to create another window which can be resized dynamically by defining its size property.

Basic Syntax

To create a new window, use the following syntax ?

new_window = Toplevel(parent_window)
new_window.geometry("widthxheight")
new_window.title("Window Title")

Example

In this example, we have created a button widget that will open a new window with a text label ?

# Import tkinter library
from tkinter import *
from tkinter import ttk

# Create an instance of tkinter frame or window
win = Tk()
# Set the geometry of tkinter frame
win.geometry("750x250")
win.title("Main Window")

# Define a new function to open the window
def open_win():
    new = Toplevel(win)
    new.geometry("750x250")
    new.title("New Window")
    # Create a Label in New window
    Label(new, text="Hey, Howdy?", font=('Helvetica', 17, 'bold')).pack(pady=30)

# Create a label
Label(win, text="Click the below button to Open a New Window", 
      font=('Helvetica', 17, 'bold')).pack(pady=30)

# Create a button to open a New Window
ttk.Button(win, text="Open", command=open_win).pack()

win.mainloop()

Output

Running the above code will display a window that contains a button widget. When we click the button, it will open a new window.

Now, click the "Open" button to open a new Window.

Key Features of Toplevel Windows

• Independent: Toplevel windows can be moved and resized independently
• Modal behavior: You can make them modal using grab_set()
• Parent relationship: When the parent window closes, child windows close automatically

Advanced Example with Modal Dialog

Here's how to create a modal dialog that blocks interaction with the parent window ?

from tkinter import *
from tkinter import ttk

def create_modal_dialog():
    dialog = Toplevel(root)
    dialog.title("Modal Dialog")
    dialog.geometry("300x150")
    
    # Make it modal
    dialog.grab_set()
    
    Label(dialog, text="This is a modal dialog", 
          font=('Arial', 12)).pack(pady=20)
    
    def close_dialog():
        dialog.grab_release()
        dialog.destroy()
    
    Button(dialog, text="Close", command=close_dialog).pack(pady=10)

root = Tk()
root.title("Main Application")
root.geometry("400x200")

Button(root, text="Open Modal Dialog", 
       command=create_modal_dialog).pack(pady=50)

root.mainloop()

Conclusion

Use Toplevel() to create new windows in tkinter applications. For modal dialogs, use grab_set() to block interaction with the parent window until the dialog is closed.