[Python] What am i doing wrong appending lists in pandas?

I have two csv files in the folder. My output for each loop iteration is avg_mtf. I have been successful in creating lists and concatenating them in the other loops within glob but my comb list is generating only 1 index. What am I doing wrong? Please help.

import pandas as pd
import glob
file_list=glob.glob('*.csv')
print (file_list);
for file in file_list:
data=pd.read_csv(file,encoding='cp1252', index_col=False, header=None)
indices=data[(data[0].str.contains('Results=3DTiltCorrMTF@Best'))&(data[0].str.contains('Tangential'))] # dataframe with all rows containing Tangential
a=indices.index.values
tan_data=[]
sag_data=[]
comb
x_axis=[]
n=a[0]+1
n=data.loc[n]
x=n.str.split(r':| ', expand=True)
x=x.iloc[:,1:-1]
x=x.T.reset_index(drop=True)
x=x.iloc[1:,:]
x=x.reset_index(drop=True)
del n

for i in a:
n=data.loc[i+2]
n=n.str.split(' ', expand=True)
n=n.iloc[:,1:-1]
tan_mtf=n.T
tan_data.append(tan_mtf)
tan_mtf=pd.concat(tan_data,axis=1,ignore_index=True)
tan_mtf=tan_mtf.reset_index(drop= True)

del i,n,a

indices=data[(data[0].str.contains('Results=3DTiltCorrMTF@Best'))&(data[0].str.contains('Sagittal'))]
a=indices.index.values
for i in a:
n=data.loc[i+2]
n=n.str.split(' ', expand=True)
n=n.iloc[:,1:-1]
sag_mtf=n.T
sag_data.append(sag_mtf)
sag_mtf=pd.concat(sag_data,axis=1,ignore_index=True)
sag_mtf=sag_mtf.reset_index(drop= True)


tan_mtf=tan_mtf.astype(float)
sag_mtf=sag_mtf.astype(float)
avg_mtf=(tan_mtf+sag_mtf)/2
comb.append(avg_mtf)

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