setting ties and constrains

[Sevketcikmaz]

I have an issue with setting ties and constrains with my strings. When I try to tie or constrain FWHM value, it says that there is an attribution error. Can you please help me solve this? The following is my strips
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import mantid algorithms, numpy and matplotlib

from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np
from CrystalField import CrystalField, CrystalFieldFit, Background, Function, PhysicalProperties
from mantid.plots.utility import MantidAxType
from mantid.api import AnalysisDataService as ADS

PPCv = PhysicalProperties('Cv')

cf = CrystalField('Er', 'D4h', B20=-0.039105620771250384, B40=-0.00012224220121308797, B44=0.005840756562690297, B60=0.00000479869319, B64=0.000030333615728, Temperature=1.5, FWHM=0.65, PhysicalProperty=[PPCv])
cf.PeakShape = 'Lorentzian'

cf.background = Background(peak=Function('Lorentzian', Amplitude=10, PeakCentre=1, FWHM=0.65),
background=Function('LinearBackground', A0=1.0, A1=0.01))

data_ws1 = Load('C:\Users\galak\OneDrive\Desktop\calculations\erpdsi_neutronECplotting_Elasticline_exclude.dat')
heat = Load('C:\Users\galak\OneDrive\Desktop\calculations\ErPd_HC.dat')

cf.peaks.constraints('f1.FWHM < 0.7', 'f2.FWHM < 0.7')

Runs the fit

fit = CrystalFieldFit(Model=cf, InputWorkspace= [data_ws1, heat])
fit.fit()

##This is Eigen values
e = cf.getEigenvalues()
print(e)

for parnames in ['B20','B40', 'B44', 'B60','B64']:
print (parnames+' = '+str(fit.model[parnames])+' meV')

table = mtd['fit_Parameters']
print ('Cost function value = '+str(table.row(table.rowCount()-1)['Value']))

#plotSpectrum('fit_Workspace',[0,1,2],error_bars=False)
#plt.xlim([1,8])
#plt.ylim([0,90])

Please help