global name is not defined

Hi all,

I'm trying to use plot.savadatatxt to save some data.

here is the MWE:
###################################################
from yade import pack, plot, export
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=.04,rRelFuzz=.2, seed =1)
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),
 NewtonIntegrator(gravity=(0,0,-9.81),damping=0.4),
]
O.dt=.5*PWaveTimeStep()
print(len(O.bodies))
def checkUnbalanced():
 if unbalancedForce()<.0001:
  O.pause()
x0 = 0.5
y0 = 0.5
z0 = 0.5
######################## sub-region and coloring#########################################
def subbox():
 global ball_list1
 ball_list1 =[]
 global b_radius
 b_radius = []
 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
      r = b.state.pos[0]
      ball_list1.append(m)
      b_radius.append(r)
      ccc = sum(b_radius)
      aaa= len(ball_list1)
 plot.addData(bbb=aaa,ddd = ccc )
 plot.saveDataTxt('ball-number.txt')
O.run(1000000,True)
###############################################

If I just use this command :plot.saveDataTxt('ball-number.txt') it works fine.
but if I just want to save the bbb data, I change the command plot.saveDataTxt('ball-number.txt') to plot.saveDataTxt('ball-number.txt',vars = bbb)

the error will be: NameError: global name 'bbb' is not defined

To my knowledge, I put the plot.savedatatxt command inside the function, why do we still need the global name?

Besides, I want to use the plot.savedatatxt to save some other information. so I made another MWE:

from yade import pack, plot, export
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=.04,rRelFuzz=.2, seed =1)
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='getdata()',iterPeriod=100),
 NewtonIntegrator(gravity=(0,0,-9.81),damping=0.4),

]
O.dt=.5*PWaveTimeStep()
print(len(O.bodies))
def checkUnbalanced():
 if unbalancedForce()<.0001:
  O.pause()
x0 = 0.5
y0 = 0.5
z0 = 0.5
######################## sub-region and coloring#########################################

def subbox():
 global ball_list1
 ball_list1 =[]
 global aaa
 global bbb
 aaa = 0.0
 bbb = 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)
      aaa= len(ball_list1)

def getdata():
 plot.addData(bbb=aaa )
 plot.saveDataTxt('ball-number.txt',vars=(bbb))

O.run(1000000,True)

##############
for this code, even though, I set the global aaa, but i still got the error:

NameError: global name 'aaa' is not defined

##########
I don't know is this related to my misunderstanding of the global variable and local variable in python or something else?

thanks in advance.

best,
yong