Error when making it a function

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This code works for my 3d graph.

But when I turn it into a function for an @interact, it does not work anymore.

How can I fix this? Thanks.

Edit: here is the code:

x, y, z = var('x, y, z')
@interact
def graphe(f = input_box(default=cos(y), label="$f(x,y)$"), r = input_box(default=10, label="$r$")):
    G = implicit_plot3d(z==f(x,y), (x, -r, r), (y, -r, r), (z, -r, r), plot_points=30, color='orange', mesh=1, opacity=.7)
    show(G, spin=1)