Visualizing cubes

I am using the following code from the examples to model cube deposition in a box, but i am not able to visualize it or export it to vtk.
This is my code:

# -*- encoding=utf-8 -*-
# 2022 © Vasileios Angelidakis <email address hidden>

# Duplicate script of cubePBscaled.py, simplified using the "potential_utils" module.

from yade import pack,
from potential_utils import *
import math

recordVTK=True
# ----------------------------------------------------------------------------------------------------------------------------
if recordVTK:
 # Create vtk directory
 import os
 import errno
 try:
  os.mkdir('./vtk/')
 except OSError as exc:
  if exc.errno != errno.EEXIST:
   raise
  pass

O.engines=[
 ForceResetter(),
 InsertionSortCollider([PotentialBlock2AABB()],verletDist=0.01),
 InteractionLoop(
  [Ig2_PB_PB_ScGeom(twoDimension=False, unitWidth2D=1.0, calContactArea=True)],
  [Ip2_FrictMat_FrictMat_KnKsPBPhys(kn_i=1e8, ks_i=1e7, Knormal=1e8, Kshear=1e7, useFaceProperties=False, viscousDamping=0.2)],
  [Law2_SCG_KnKsPBPhys_KnKsPBLaw(label='law',neverErase=False, allowViscousAttraction=True, traceEnergy=False)]
 ),
 NewtonIntegrator(damping=0.0,exactAsphericalRot=True,gravity=[0,-9.81,0]),
    # save data for Paraview
    VTKRecorder(fileName='3d-vtk-', recorders=['all'], iterPeriod=1000),
]

powderDensity = 2000
meanSize = 1.0
distanceToCentre = meanSize/2.
wallThickness = 0.5*meanSize

O.materials.append(FrictMat(young=-1,poisson=-1,frictionAngle=radians(0.0),density=powderDensity,label='frictionless')) #The normal and shear stifness values are determined in the IPhys functor, thus the young, poisson parameters of the FrictMat are not used.
lengthOfBase = 9.0*meanSize
heightOfBase = 14.0*meanSize
sp=pack.SpherePack()
mn,mx=Vector3(-0.5*(lengthOfBase-wallThickness),0.5*meanSize,-0.5*(lengthOfBase-wallThickness)),Vector3(0.5*(lengthOfBase-wallThickness),7.0*heightOfBase,0.5*(lengthOfBase-wallThickness))
R=sqrt(3.0)*distanceToCentre
sp.makeCloud(mn,mx,R,0,100,False)

r=0.01*meanSize
for s in sp:
 color=Vector3(random.random(),random.random(),random.random())
 # PB_utils.cuboid
 b=cuboid(material=O.materials['frictionless'], edges=[1.0,1.0,1.0], r=r, R=0.0, center=s[0], mask=1, isBoundary=False, fixed=False, color=color)
 b.state.ori = Quaternion((random.random(),random.random(),random.random()),random.random()) #s[2]
 O.bodies.append(b)

#Bottom faces of the box
r=0.1*wallThickness
color=[0,0.5,1]

# Centroids of particles forming the bottom face of the box
center= [[ 0, 0, 0],
  [-lengthOfBase/3.0, 0, 0],
  [ lengthOfBase/3.0, 0, 0],

  [ 0, 0, -lengthOfBase/3.0],
  [-lengthOfBase/3.0, 0, -lengthOfBase/3.0],
  [ lengthOfBase/3.0, 0, -lengthOfBase/3.0],

  [ 0, 0, lengthOfBase/3.0],
  [-lengthOfBase/3.0, 0, lengthOfBase/3.0],
  [ lengthOfBase/3.0, 0, lengthOfBase/3.0]
 ]

edges=[lengthOfBase/3.,wallThickness,lengthOfBase/3.]

lidID=len(O.bodies)
for i in range(0,9):
 O.bodies.append( cuboid(material=O.materials['frictionless'], edges=edges, r=r, R=0.0, center=center[i], mask=3, isBoundary=True, fixed=True, color=color) )

# Vertical faces A-B-C-D of the box
center= [ [ 0, 0.5*heightOfBase, 0.5*lengthOfBase],
   [ 0, 0.5*heightOfBase, -0.5*lengthOfBase],
   [ 0.5*lengthOfBase, 0.5*heightOfBase, 0],
   [-0.5*lengthOfBase, 0.5*heightOfBase, 0]
 ]

edges= [ [ lengthOfBase, heightOfBase, wallThickness],
   [ lengthOfBase, heightOfBase, wallThickness],
   [wallThickness, heightOfBase, lengthOfBase],
   [wallThickness, heightOfBase, lengthOfBase]
 ]

transparentID=len(O.bodies)
for i in range(0,4):
 O.bodies.append( cuboid(material=O.materials['frictionless'], edges=edges[i], r=r, R=0.0, center=center[i], mask=3, isBoundary=True, fixed=True, color=color) )
O.bodies[transparentID].shape.wire=True

escapeNo=0
def myAddPlotData():
 global escapeNo
 global wallThickness
 global meanSize
 uf=utils.unbalancedForce()
 if isnan(uf):
  uf = 1.0
 KE = utils.kineticEnergy()

 for b in O.bodies:
  if b.state.pos[1] < -5.0*meanSize and len(b.state.blockedDOFs)==0: #i.e. fixed==False
   escapeNo = escapeNo+1
   O.bodies.erase(b.id)
 if O.iter>15000:
  removeLid()
 plot.addData(timeStep1=O.iter,timeStep2=O.iter,timeStep3=O.iter,timeStep4=O.iter,time=O.time,unbalancedForce=uf,kineticEn=KE,outsideNo=escapeNo)

from yade import plot
plot.plots={'timeStep1':('unbalancedForce'),'timeStep2':('kineticEn'),'time':('outsideNo')}
#plot.plot() #Uncomment to view plots
O.engines=O.engines+[PyRunner(iterPeriod=10,command='myAddPlotData()')]

def removeLid():
 global lidID
 if (O.bodies[lidID]):
  O.bodies.erase(lidID)

O.dt = 0.2*sqrt(0.3*O.bodies[0].state.mass/1.0e8)

# ----------------------------------------------------------------------------------------------------------------------------
if recordVTK:
 # Take snapshots
# O.engines=O.engines+[SnapshotEngine(iterPeriod=100,fileBase='vtk/jenga-',firstIterRun=10,label='snapshooter')]

 # Export VTK results
 from yade import export
 vtkExporter = export.VTKExporter('./vtk/cubePBscaled')

 def vtkExport():
  vtkExporter.exportPotentialBlocks(what=dict(n='b.id'))

 O.engines=O.engines+[PyRunner(iterPeriod=500,command='vtkExport()')]

from yade import qt
qt.Controller()
v=qt.View()

O.saveTmp()

thank you!