Question

I have a window whose content changes. Sometimes the content is larger than the window, so the window expands to fit it’s children. However, when I center a window using a call to “geometry”, the window no longer resizes. Below, you will find code that illustrates this.

If you comment out the delayed center() function call, you’ll notice that the window expands to fit its content. If you leave it as is, the window centers, but no longer expands to fit its content.

Is it possible to center a window AND have it continue to resize to fit its content?

from Tkinter import *
import ttk

def center(root):
    w = root.winfo_screenwidth()
    h = root.winfo_screenheight()
    rootsize = tuple(int(_) for _ in root.geometry().split('+')[0].split('x'))
    x = w/2 - rootsize[0]/2
    y = h/2 - rootsize[1]/2
    root.geometry("%dx%d+%d+%d" % (rootsize + (x, y)))

root = Tk()
var = StringVar()
var.set('Small Text')

label = ttk.Label(root, textvariable=var)
label.grid(column=0, row=0)

# Change the text label in a couple of seconds.
def changeit():
    var.set('BIG TXT - ' * 5)
root.after(2000, changeit)

# Comment out this center call and the label expands.
root.after(100, lambda: center(root))
root.mainloop()

Answer 1

When you call the geometry command, don’t provide a width and height — just supply the x/y values. When you give it an explicit width and height, you’re telling Tk “I want the window to be exactly this size” so it turns it’s auto-resize behavior off.

root.geometry("+%d+%d" % (rootsize + (x, y)))

Also, you can use winfo_width() and winfo_height() to get the actual size of the window, instead of parsing the output of the geometry method.