One could set the size of a window (be it a Tk instance or Toplevel instance) using geometry method:
# identical to root.geometry('256x512')
root.geometry('{}x{}'.format(256, 512))
or:
# identical to window.geometry('512x256')
window.geometry('{}x{}'.format(512, 256))
Additionally using geometry method one could also determine the upper-left corner of a window:
window.geometry('+{}+{}'.format(16, 32))
or perhaps both at once:
#identical to window.geometry('512x256+16+32')
window.geometry('{}x{}+{}+{}'.format(512, 256, 16, 32))
More generally one could use winfo_toplevel in order to easily set the size of the window from its children:
widget.winfo_toplevel().geometry('{}x{}+{}+{}'.format(512, 256, 16, 32))
Example
Here's an example that sets both the size and placement coordinates of a window through a children widget's reference:
try:                        # In order to be able to import tkinter for
    import tkinter as tk    # either in python 2 or in python 3
except ImportError:
    import Tkinter as tk
def on_button_press(widget):
    width = 512
    height = 256
    x = 16
    y = 32
    widget.winfo_toplevel().geometry('{}x{}+{}+{}'.format(width, height, x, y))
if __name__ == '__main__':
    root = tk.Tk()
    window = tk.Toplevel(root)
    button = tk.Button(window, text="Resize & Place")
    #the line below is related to calling a method when a button is pressed
    button['command'] = lambda w=button: on_button_press(w)
    button.pack()
    tk.mainloop()