CODE EXAMPLE FOR PYTHON

make widget span window width tkinter

import tkinter
import tkinter.ttk

win = tkinter.Tk()
win.geometry('600x600')

frame = tkinter.Frame(win, bg='red', height=300)
frame.grid(row=0, column=0, sticky='ew')
win.grid_columnconfigure(0,weight=1)

win.mainloop()