can we set a mask for a particular particle

Hi All,

I want to use this command : yade.export.text(filename, mask=-1) to export the particle position and radius. the explanation for this command is: mask (int) – export only spheres with the corresponding mask.

here is the MWE:

import numpy as np
from yade import pack, plot, export, utils
import math
O.bodies.append(geom.facetBox((.5,.5,.5),(.5,.5,.5),wallMask=31))
sp=pack.SpherePack()
sp.makeCloud((0,0,0),(1,1,1),rMean=.07,rRelFuzz=.5)
sp.toSimulation()
O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb()]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom(),Ig2_Facet_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_FrictPhys()],
  [Law2_ScGeom_FrictPhys_CundallStrack()]
 ),
 PyRunner(command='checkUnbalanced()',realPeriod=2),
 PyRunner(command='subbox()',iterPeriod=1000),
 #PyRunner(command='displacement()',iterPeriod=30000),
 #VTKRecorder(fileName='3d-vtk-',recorders=['all','bstresses'],iterPeriod=1000),
 PyRunner(command='get_po()',iterPeriod=1000),
 NewtonIntegrator(gravity=(0,0,-9.81),damping=0.4),

]
O.dt=.5*PWaveTimeStep()
print(len(O.bodies))
def checkUnbalanced():
 if unbalancedForce()<.001:
  O.pause()
#plot.plots={'i':('unbalanced')}
#plot.plot()
x0 = 0.5
y0 = 0.5
z0 = 0.5
######################## sub-region and coloring#########################################
ball_list1 =[]
def subbox():
 global ball_list1
 aaa = 0.0
 for b in O.bodies:
  brp = math.sqrt((b.state.pos[0]-x0)**2 + (b.state.pos[1]-y0)**2)
  if brp >= 0.2:
   if brp <= 0.4:
    if (b.state.pos[2]-z0 >= -0.5) and (b.state.pos[2]-z0 <= 0.0):
     if isinstance(b.shape,Sphere):
      b.shape.color =Vector3(255,255,255) # white
      m = b.id
      ball_list1.append(m)
for i in ball_list1:
 for b in O.bodies[i]:
  b.mask = 1
def get_po():
 export.text(filename = "state1.txt",mask = 1)

but it seems this command just export all particle' information. not just ball_list1.

Is there anyone can give me some suggestions.

best,
yong