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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 circle_level_set(image_shape, center=None, radius=None):
 """Create a circle level set with binary values. Parameters image_shape : tuple of positive integers Shape of the image center : tuple of positive integers, optional Coordinates of the center of the circle given in (row, column). If not given, it defaults to the center of the image. radius : float, optional Radius of the circle. If not given, it is set to the 75% of the smallest image dimension. Returns ------- out : array with shape `image_shape` Binary level set of the circle with the given `radius` and `center`. See also -------- checkerboard_level_set """


    if center is None:
        center = tuple(i // 2 for i in image_shape)

    if radius is None:
        radius = min(image_shape) * 3.0 / 8.0

    grid = np.mgrid[[slice(i) for i in image_shape]]
    grid = (grid.T - center).T
    phi = radius - np.sqrt(np.sum((grid)**2, 0))
    res = np.int8(phi > 0)
    return res