How to use the chempy.cpv.scale function in chempy

def planeFromPoints(point1, point2, point3, facetSize):
    v1 = cpv.normalize(cpv.sub(point2, point1))
    v2 = cpv.normalize(cpv.sub(point3, point1))
    normal = cpv.cross_product(v1, v2)
    v2 = cpv.cross_product(normal, v1)
    x = cpv.scale(v1, facetSize)
    y = cpv.scale(v2, facetSize)
    center = point2
    corner1 = cpv.add(cpv.add(center, x), y)
    corner2 = cpv.sub(cpv.add(center, x), y)
    corner3 = cpv.sub(cpv.sub(center, x), y)
    corner4 = cpv.add(cpv.sub(center, x), y)
    return plane(corner1, corner2, corner3, corner4, normal)

def visualize_orientation(direction, center=[0, 0, 0], scale=1.0, symmetric=False, color='green', color2='red'):
    '''
    Draw an arrow. Helper function for "helix_orientation" etc.
    '''
    from pymol import cgo
    color_list = cmd.get_color_tuple(color)
    color2_list = cmd.get_color_tuple(color2)
    if symmetric:
        scale *= 0.5
    end = cpv.add(center, cpv.scale(direction, scale))
    radius = 0.3
    obj = [cgo.SAUSAGE]
    obj.extend(center)
    obj.extend(end)
    obj.extend([
        radius,
        0.8, 0.8, 0.8,
    ])
    obj.extend(color_list)
    if symmetric:
        start = cpv.sub(center, cpv.scale(direction, scale))
        obj.append(cgo.SAUSAGE)
        obj.extend(center)
        obj.extend(start)
        obj.extend([
            radius,

if symmetric:
        scale *= 0.5
    end = cpv.add(center, cpv.scale(direction, scale))
    radius = 0.3

    obj = [cgo.SAUSAGE]
    obj.extend(center)
    obj.extend(end)
    obj.extend([
        radius,
        0.8, 0.8, 0.8,
    ])
    obj.extend(color_list)

    if symmetric:
        start = cpv.sub(center, cpv.scale(direction, scale))
        obj.append(cgo.SAUSAGE)
        obj.extend(center)
        obj.extend(start)
        obj.extend([
            radius,
            0.8, 0.8, 0.8,
        ])
        obj.extend(color2_list)

    coneend = cpv.add(end, cpv.scale(direction, 4.0*radius/cpv.length(direction)))
    obj.append(cgo.CONE)
    obj.extend(end)
    obj.extend(coneend)
    obj.extend([
        radius * 1.75,
        0.0,

def _common_orientation(selection, vec, visualize=1, quiet=0):
    '''
    Common part of different helix orientation functions. Does calculate
    the center of mass and does the visual feedback.
    '''
    stored.x = []
    cmd.iterate_state(-1, '(%s) and name CA' % (selection),
            'stored.x.append([x,y,z])')
    if len(stored.x) < 2:
        print 'warning: count(CA) < 2'
        raise CmdException
    center = cpv.scale(_vec_sum(stored.x), 1./len(stored.x))
    if visualize:
        scale = cpv.distance(stored.x[0], stored.x[-1])
        visualize_orientation(vec, center, scale, True)
        cmd.zoom(selection, buffer=2)
    if not quiet:
        print 'Center: (%.2f, %.2f, %.2f) Direction: (%.2f, %.2f, %.2f)' % tuple(center + vec)
    return center, vec