def bounding_box(positions):
    '''Computes the bounding box for a list of 3-dimensional points.
    '''
    (x0, y0, z0) = (x1, y1, z1) = positions[0]
    for x, y, z in positions:
        x0 = min(x0, x)
        y0 = min(y0, y)
        z0 = min(z0, z)
        x1 = max(x1, x)
        y1 = max(y1, y)
        z1 = max(z1, z)
    return (x0, y0, z0), (x1, y1, z1)
Computes the bounding box for a list of 3-dimensional points.