def sfi(nb_pts, les_cas):
    x_pts = [0]
    y_pts = [0]

    for i in range(nb_pts):
        tirage = random()

        for (p, A, V) in les_cas:
            if tirage < p:
                x_dernier  = x_pts[-1]
                y_dernier  = y_pts[-1]

                x = A[0]*x_dernier + A[1]*y_dernier + V[0]
                y = A[2]*x_dernier + A[3]*y_dernier + V[1]

                x_pts.append(x)
                y_pts.append(y)

                break

    return (x_pts, y_pts)

nb_pts = 20000

les_cas = [
# Cas 1
    (
        0.5,
        [0.5, -0.5, 0.5, 0.5],
        [0, 0]
    ),
# Cas 2 : 1 = 0.5 + 0.5
    (
        1,
        [-0.5, -0.5, 0.5, -0.5],
        [1, 0]
    )
]

%time x_pts, y_pts = sfi(nb_pts, les_cas)
%time plot(points(zip(x_pts, y_pts)), '.')

%time show(plot(points(zip(x_pts, y_pts)), '.'), svg=False, figsize=3)