def f(x):
    return  x**3 - 2*x - 1

def dfdx(x):
    return 3*x**2 - 2

val = 0.00001
x_n = 1.0

while abs(f(x_n)) > val:

    x_np1 = x_n - f(x_n)/dfdx(x_n)
    x_s = x_np1
    print('x_s = ', x_s)
    x_n = x_np1  # Shift