Homogenization for stress and strain in abaqus python script

Dear All,
I have a simple 2D model which I would like to get stress and strain components in each frame of each step, and then calculate the average in each frame by dividing over all elements.I have write such a code:

def write_res():
global a
a = np.array([])
odb = openOdb(abq_job+'.odb', readOnly=True)
ubc = np.zeros(2)
elementset=odb.rootAssembly.instances['PART-1-1'].elements
n_elements=len(elementset)
s11 = np.zeros(n_elements)
s22 = np.zeros(n_elements)
s33 = np.zeros(n_elements)
s12 = np.zeros(n_elements)

Le11 = np.zeros(n_elements)
Le22 = np.zeros(n_elements)
Le33 = np.zeros(n_elements)
Le12 = np.zeros(n_elements)

ep11 = np.zeros(n_elements)
ep22 = np.zeros(n_elements)
ep33 = np.zeros(n_elements)
ep12 = np.zeros(n_elements)
with open(path_r+f_name,'a') as f:
for step in odb.steps.values(): # iterate through all the steps in the ODB
for frame in step.frames: # iterate through all the frames in the step
field_stress = frame.fieldOutputs['S']
field_strain = frame.fieldOutputs['LE']
field_plastic_strain =frame.fieldOutputs['PE']
# Get the subset of the stress and strain field data for the element set
subfield_stress = field_stress.getSubset(region=odb.rootAssembly.instances['PART-1-1'])
subfield_strain = field_strain.getSubset(region=odb.rootAssembly.instances['PART-1-1'])
subfield_plastic_strain=field_plastic_strain.getSubset(region=odb.rootAssembly.instances['PART-1-1'])
ubc[0] = xload
ubc[1] = yload
# Loop over all stress and strain field data in the subset
for i, value in enumerate(subfield_stress.values):
s11 = value.data[0]
s22 = value.data[1]
s33 = value.data[2]
s12 = value.data[3]

Le11 = subfield_strain.values.data[0]
Le22 = subfield_strain.values.data[1]
Le33 = subfield_strain.values.data[2]
Le12 = subfield_strain.values.data[3]

ep11 = subfield_plastic_strain.values.data[0]
ep22 = subfield_plastic_strain.values.data[1]
ep33 = subfield_plastic_strain.values.data[2]
ep12 = subfield_plastic_strain.values.data[3]

# Calculate the average stress components for each element for the current frame
s11_avg = sum(s11)/n_elements
s22_avg = sum(s22)/n_elements
s33_avg = sum(s33)/n_elements
s12_avg = sum(s12)/n_elements
Le11_avg = sum(Le11)/n_elements
Le22_avg = sum(Le22)/n_elements
Le33_avg = sum(Le33)/n_elements
Le12_avg = sum(Le12)/n_elements
ep11_avg = sum(ep11)/n_elements
ep22_avg= sum(ep22)/n_elements
ep33_avg= sum(ep33)/n_elements
ep12_avg= sum(ep12)/n_elements

# Append the results to the row variable
row = [s11_avg, s22_avg, s33_avg, s12_avg, Le11_avg, Le22_avg, Le33_avg, Le12_avg, ep11_avg, ep22_avg, ep33_avg, ep12_avg,ubc[0],ubc[1]]
a=np.append(a,row)
a.tofile(f, sep=';', format='%12.5e')
f.write('\n')

return None
Bu when I open the CSV, instead of having for each row average of each component, the values decrease sequentially in each row. Can you please tell me where I have a code mistake? or whether it is true or not.
Thank!