quasi-affine subvarieties

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I would like to set up a quasi-affine variety in $\mathbb{A}^2$ (over a field of characteristic zero). I contend with QQbar:

n=2
A.<x,y>= AffineSpace(QQbar, n)
X = Curve([y^2 -x^3], A)

$X$ is a affine variety. How did I remove one point at $(0,0)$ from $X$ which would result in a quasi-affine subvariety? What are the options in sagemath?

(By the way, I may choose CC or alternatively QQbar for the underlying field.)