from turtle import Turtle

def draw_square(turtle, length):
    for _ in range(4):
        turtle.forward(length)
        turtle.right(90)

def draw_filled_square(turtle, length):
    turtle.begin_fill()
    draw_square(turtle, length)
    turtle.end_fill()

Turtle.draw_filled_square = draw_filled_square
sophia = Turtle()
sophia.fillcolor('red')
sophia.draw_filled_square(100)

sophia.screen.mainloop()