[Tkinter] Button won't execute function

[TheLegendOfPanda]

I programming the game battleships and got stuck when it came to the user input for the fields you want to shoot on. For that I created a tkinter window, which should take the user input given when 'ok' is pressed. When pressed, the programm should also check how many of that sized ship are left etc. and than obviously change the labels on the window (the absolute amount of them is already given, the numbers are an example). When i press 'ok', nothing happens and I don't know why. Thank you in advance.

import tkinter as tk
root = tk.Tk()
board_size = 10
c5a = 1          # amount of ships size 5
b4a = 2          # -"- 4
c3a = 3          # -"- 3
d2a = 4          # -"- 2
index = 0

class ShipPlacementPlayer:
    
    def placement():
        ship_list = ('Carrier (5)', 'Battleship (4)', 'Cruiser (3)', 'Destroyer (2)')
        global board_size, c5a, b4a, c3a, d2a, index
        sa = [c5a, b4a, c3a, d2a]
        sl = sa[index]                    # ships left
        current_ship = ship_list[index]
        
        if sl != 0:
            ship = tk.Label(root, text=current_ship, font=(15), bg='white')
            ship.grid(row=1, column=0)
            left = tk.Label(root, text=str(sl)+' left', font=(15), bg='white')
            left.grid(row=1, column=1)
            
            if index == 0:
                c5a -= 1
                return c5a
            elif index == 1:
                b4a -= 1
                return b4a
            elif index == 2:
                c3a -= 1
                return c3a
            elif index == 3:
                d2a -= 1
                return d2a
        else:
            index += 1
            return index
            ship.destroy()
            left.destroy()
            
            ship = tk.Label(root, text=current_ship, font=(15), bg='white')
            ship.grid(row=1, column=0)
            left = tk.Label(root, text=str(sl)+' left', font=(15), bg='white')
            left.grid(row=1, column=1)
            
            if index == 0:
                c5a -= 1
                return c5a
            elif index == 1:
                b4a -= 1
                return b4a
            elif index == 2:
                c3a -= 1
                return c3a
            elif index == 3:
                d2a -= 1
                return d2a
        
    def window(*args):
        global board_size
        root.title('Ship placement')
        w = 215; h = 192
        ws = root.winfo_screenwidth(); hs = root.winfo_screenheight()
        x = (ws/2) - (600+w/2); y = (hs/2) - (h/2)
        root.geometry('%dx%d+%d+%d' % (w, h, x, y))
        root.configure(background='white')
        root.attributes("-topmost", True)

        place_label = tk.Label(root, text=' Place your ships! ', font=(15), fg='white', bg='black')
        place_label.grid(row=0, columnspan=2)
        
        emptyplace = tk.Label(root, font=(15), bg='white')
        emptyplace.grid(row=1, columnspan=2)
        
        vh = tk.IntVar()
        v = tk.Radiobutton(root, text='Vertical', variable=vh, value=1, font=(10), bg='alice blue')
        v.grid(row=2, column=0)
        h = tk.Radiobutton(root, text='Horizontal', variable=vh, value=2, font=(10), bg='alice blue')
        h.grid(row=2, column=1)
        
        abc_list = ('A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
               'Q','R','S','T','U','V','W','X','Y','Z')
        abc_list_bs = abc_list[:board_size]
        
        label_row = tk.Label(root, text='Row:', font=(15), bg='white')
        label_row.grid(row=4, column=0, sticky='E')
        label_column = tk.Label(root, text='Column:', font=(15), bg='white')
        label_column.grid(row=5, column=0, sticky='E')
        
        rowi = tk.Spinbox(root, values=sorted(abc_list_bs), font=(15), width=3)
        rowi.grid(row=4,column=1)
        columni = tk.Spinbox(root, from_=0, to=board_size, font=(15), width=3)
        columni.grid(row=5,column=1)
        
        okp = tk.Button(root,text='OK', font=(15), fg='white', bg='black', command=ShipPlacementPlayer.placement())
        okp.grid(row=6,columnspan=2)
        
app = ShipPlacementPlayer.window()
root.mainloop()