How can i center a button above the window in Python using only tkinter and grid?

When i tried to center my button, it didn't center perfectly above the window. I tried almost everything but it went to right or left, not in the middle of the window.

I was expecting it to be placed in the middle of the window.

The trick is to make sure that the allocated space is in the center of the window. By default, the widgets in a grid only take up the least amount of space necessary. Thus, if you have a window that is 500 pixels wide but have three 100 pixel columns, the widgets will only fill 300 pixels of space, leaving the rest unused.

The solution is to make sure that at least one column will grow and shrink so that the entire window is being used. You do this with columnconfigure and the weight option. Giving a column a non-zero weight will cause it to use up unused space.

Here's the simplest example of that in action. Notice that we have a single column, and we've given that column a weight of 1. That means that all unused space is allocated to that column. Also notice that by default the button is centered in the space allocated to it. You can resize the window to any size you want and the button will remain centered.

import tkinter as tk

root = tk.Tk()
button = tk.Button(root, text="Center Button")
button.grid(row=0, column=0)
root.grid_columnconfigure(0, weight=1)

root.mainloop()

The difficulty comes when having multiple columns of different sizes. Even that has a fairly simple solution. If you want only the button to be in the top row, have the row span all columns, which you can do with the columnspan option.

The following example adds five columns of varying widths, and each with a different weight causing them to each expand a different amount.

import tkinter as tk

root = tk.Tk()

# create five columns, each with a different size
for i in range(4):
    label = tk.Label(root, text=f"Column {i}")
    label.grid(row=1, column=i)
    root.columnconfigure(i, weight=i)
    
# add the button in the first row, and have it centered
# over all other rows
button = tk.Button(root, text="Center Button")
button.grid(row=0, column=0, columnspan=5)

root.mainloop()

For more information, see the question What does 'weight' do in tkinter?