How to use the vpython._vector_import_helper.norm function in vpython

def convert(pos=(0,0,0), up=(0,1,0), points=None, closed=True):
        pos = vector(pos)
        up = norm(vector(up))
        up0 = vector(0,1,0)
        angle = acos(up.dot(up0))
        reorient = (angle > 0.0)
        axis = up0.cross(up)
        pts = []
        for pt in points:
            newpt = vector(pt[0],0,-pt[1])
            if reorient: newpt = newpt.rotate(angle=angle, axis=axis)
            pts.append(pos+newpt)
        if closed and not pts[-1].equals(pts[0]): pts.append(pts[0])
        return pts

lm = mag(p2 - p1)
        if (lm < L):
            L = lm

    r = L * roundness # radius of rounded curve connecting adjacent sides

    ncp = [[0,0]] # starting point will be modified later
    for i in range(lcp):
        v1 = cp[(i+1) % lcp] - cp[i % lcp]   # first side
        v2 = cp[(i+2) % lcp] - cp[(i+1) % lcp] # next side
        theta = v1.diff_angle(v2)   # angle of change of direction from first side to next side
        d = r*tan(theta/2)         # how much to shorten the end of a side and the start of the next
        p1 = cp[i] + v1 - d*norm(v1)   # end of first side, start of bend
        p2 = cp[(i+1) % lcp] + d*norm(v2) # start of next side, end of bend
        ncp.append([p1.x, p1.y])
        N = norm(v1).cross(norm(v2))
        center = p1 + r*norm(N.cross(v1)) # center of circular arc
        v = p1 - center
        dtheta = theta/(nseg+1)
        if N.z < 0: dtheta = -dtheta
        if invert:
            c = 0.5*(p1 + p2) # midpoint along line connecting p1 and p2
            center = c + (c-center)    # move center to other side of corner
            v = p1 - center
            dtheta = -dtheta

        for j in range(1,nseg): # don't repeat the starting point of this arc
            v1 = center + v.rotate(j*dtheta)
            ncp.append([v1.x, v1.y])

        ncp.append([p2.x, p2.y])

p1 = cp[i]
        p2 = cp[(i + 1) % lcp]
        lm = mag(p2 - p1)
        if (lm < L):
            L = lm

    r = L * roundness # radius of rounded curve connecting adjacent sides

    ncp = [[0,0]] # starting point will be modified later
    for i in range(lcp):
        v1 = cp[(i+1) % lcp] - cp[i % lcp]   # first side
        v2 = cp[(i+2) % lcp] - cp[(i+1) % lcp] # next side
        theta = v1.diff_angle(v2)   # angle of change of direction from first side to next side
        d = r*tan(theta/2)         # how much to shorten the end of a side and the start of the next
        p1 = cp[i] + v1 - d*norm(v1)   # end of first side, start of bend
        p2 = cp[(i+1) % lcp] + d*norm(v2) # start of next side, end of bend
        ncp.append([p1.x, p1.y])
        N = norm(v1).cross(norm(v2))
        center = p1 + r*norm(N.cross(v1)) # center of circular arc
        v = p1 - center
        dtheta = theta/(nseg+1)
        if N.z < 0: dtheta = -dtheta
        if invert:
            c = 0.5*(p1 + p2) # midpoint along line connecting p1 and p2
            center = c + (c-center)    # move center to other side of corner
            v = p1 - center
            dtheta = -dtheta

        for j in range(1,nseg): # don't repeat the starting point of this arc
            v1 = center + v.rotate(j*dtheta)
            ncp.append([v1.x, v1.y])

def line(self, pos=[0,0], width=1, height=None, np=2, rotate=0, thickness=None,
                    start=[0,0], end=[0,1], scale=1, xscale=1, yscale=1):
        v = vec(end[0] - start[0], end[1] - start[1], 0)
        if thickness is None: thickness = .01 * mag(v)
        dv = thickness * norm(vec(0, 0, 1).cross(v))
        dx = dv.x
        dy = dv.y
        cp = []   # outer line
        cpi = []  # inner line
        vstart = vec(start[0], start[1], 0)
        v = vec(end[0]-start[0], end[1]-start[1], 0)
        vline = v/(floor(np-1))
        for i in range(np):
            v = i*vline
            x = start[0] + v.x
            y = start[1] + v.y
            cp.append([x + pos[0], y + pos[1]])
            cpi.append([x + pos[0] + dx, y + pos[1] + dy])

        cpi.reverse()
        for i in range(len(cpi)): cp.append(cpi[i])

dtheta = theta/(nseg+1)
        if N.z < 0: dtheta = -dtheta
        if invert:
            c = 0.5*(p1 + p2) # midpoint along line connecting p1 and p2
            center = c + (c-center)    # move center to other side of corner
            v = p1 - center
            dtheta = -dtheta

        for j in range(1,nseg): # don't repeat the starting point of this arc
            v1 = center + v.rotate(j*dtheta)
            ncp.append([v1.x, v1.y])

        ncp.append([p2.x, p2.y])

    v1 = cp[1] - cp[0]
    v1 = cp[0] + d*norm(v1) # start of first side, at end of preceding bend
    ncp[0] = [v1.x, v1.y]
    return ncp