from sympy import *
from spb import *
x, y, a, b = symbols("x y a b")
expr = (cos(x) + a * sin(x) * sin(y) - b * sin(x) * cos(y))**2
plot_contour(expr, (x, 0, pi), (y, 0, 2 * pi),
    params={a: (1, 0, 2), b: (1, 0, 2)},
    grid=False, use_latex=False)