How to solve the issue 'a float is required' when using the mathfunction log

Hello,I'm going to use yade to simulate biaxial drained compression experiment. But when it runs to script 46,strainy = -100.*math.log(O.cell.trsf[1]), the runner will report an error, a float is required.I'm very confused on the function log I use.
Could you please help me solve the error?
Thank you.

Here are my scripts and I use python 2.7.15.
from yade import pack,plot
import math

O.materials.append(FrictMat(young=6.e8,poisson=.8,frictionAngle=.0))

sp = pack.SpherePack()
size = .24
sp.makeCloud(minCorner=(0,0,.05),maxCorner=(size,size,.05),rMean=.005,rRelFuzz=.4,num=400,periodic=True,seed=1)
sp.toSimulation()
O.cell.hSize = Matrix3(size,0,0, 0,size,0, 0,0,.1)
print len(O.bodies)
for p in O.bodies:
   p.state.blockedDOFs = 'zXY'
   p.state.mass = 2650 * 0.1 * pi * p.shape.radius**2 # 0.1 = thickness of cylindrical particle
   inertia = 0.5 * p.state.mass * p.shape.radius**2
   p.state.inertia = (.5*inertia,.5*inertia,inertia)

O.dt = utils.PWaveTimeStep()
print O.dt

O.engines = [
   ForceResetter(),
   InsertionSortCollider([Bo1_Sphere_Aabb()]),
   InteractionLoop(
      [Ig2_Sphere_Sphere_ScGeom()],
      [Ip2_FrictMat_FrictMat_FrictPhys()],
      [Law2_ScGeom_FrictPhys_CundallStrack()]
   ),
   PeriTriaxController(
      dynCell=True,
      goal=(-1.e5,-1.e5,0),
      stressMask=3,
      relStressTol=.001,
      maxUnbalanced=.001,
      maxStrainRate=(.5,.5,.0),
      doneHook='shear()',
      label='biax'
   ),
   NewtonIntegrator(damping=0.1),
   PyRunner(command='saveAddData()',iterPeriod=200)
]

def saveAddData():
   stress = utils.getStress()
   plot.addData(
      strainy = -100.*math.log(O.cell.trsf[1]),
      stressy = -0.001*stress[1],
      p = -0.0005*(stress[0]+stress[1]),
      q = 0.0005*(stress[0]-stress[1])
   )
   plot.saveDataTxt('drained.txt',vars=('strainy','stressy','p','q'))

def shear():
   print getStress()
   print O.cell.hSize
   setContactFriction(0.5)
   O.cell.trsf=Matrix3.Identity
   biax.goal=(-1.e5,-1.e-1,0)
   biax.stressMask=1
   biax.relStressTol=0.01
   biax.maxUnbalanced=0.01
   biax.maxStrainRate=(0.01,0.01,0)
   O.engines=O.engines+[PyRunner(command='saveAddData()',iterPeriod=200)]
   O.pause()

O.run();O.wait()

The error it reports is as follows.
/usr/bin/yadedaily in <module>()

/usr/bin/yadedaily in saveAddData()
     44 stress = utils.getStress()
     45 plot.addData(
---> 46 strainy = -100.*math.log(O.cell.trsf[1]),
     47 stressy = -0.001*stress[1],
     48 p = -0.0005*(stress[0]+stress[1]),

TypeError: a float is required