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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def prox_circle(xy, step):
 """Projection onto circle"""

    center = np.array([0,0])
    dxy = xy - center
    radius = 0.5
    # exclude interior of circle
    #if (dxy**2).sum() < radius**2:
    # exclude everything other than perimeter of circle
    if 1:
        phi = np.arctan2(dxy[1], dxy[0])
        return center + radius*np.array([np.cos(phi), np.sin(phi)])
    else:
        return xy