import glob
import pandas as pd

variable_1 = glob.glob('dir_pathway/*txt')
variable_2 = glob.glob('other_dir_pathway/*txt')

def my_function(variable_arg):
    ## a bunch of code to get certain things from the directory ##
    variable_3 = pd.DataFrame( ## stuff taken from directory ## )
    variable_3.to_csv(variable_arg + "_add_var_to_me.txt")