how to append dataframe in loop

Question

I am only getting the last loop result

`

txt_files = glob.glob(path + '101-200/101-200/2000-2019/*/*.txt')

df = pd.DataFrame()

for i in txt_files:
    doc_series = []
    filename_series = []
    filename_series.append(i.split('.txt')[0].split('\\')[-1])
    with open(i,"r") as text_file:
        doc_series.append(text_file.read())
    
    dataframe = build_aux_metrics1(filename_series, doc_series)

    df = pd.concat([df, dataframe])

df.to_csv('aux_metrics_2000_2019.csv', index = False)

`

I want after every loop run the result should be appended to the dataframe