Extracting Load proportionality factor (LPF) from odb file in ABAQUS using python script

Dear firends,
I run some abaqus input files and got my odb files(for example 100 odb files in a specific folder with the name of try). I want to extract LPF (load proportionality factor for whole model) using python script (In my analysis I used static riks). I used the following commands but when I run my script I get an error :

#!usr/bin/python
from abaqusConstants import*
from odbAccess import*
import string
import sys, os
import glob
FOLDER="C:/ABAQUS_WORK/try"
os.chdir(FOLDER)
for filename in glob.glob('*odb'):
    odb=session.openOdb(name=filename)
    session.XYDataFromHistory(name='LoadFactor',odb=odb,outputVariableName='Load propotionality factor:LPF for Whole Model',steps=('apply load',))
    x0=session.xyDataObjects['LoadFactor']
    session.writeXYReport(fileName="C:\\ABAQUS_WORK\try\LoadFactor.dat",xyData=(x0,)) 
session.odbs[filename].close()

 The error is:XypError:History output cannot be located for the variable'Load propotionality factor:LPF for Whole Model' in the step(s) specified
Does anyone know why I got this error ?or dose anyone have a python script to extract LPF which I can follow ?It will really help me to go further in my research. Thanks in advanced.

Shabnam