The script to output files in which the substring is not found

unfinder.py

import os
import io
import argparse
 
def unfind_substr(directory, word): 
    files = os.listdir(directory)
    finalFiles = [] 
    for file in files:
        filename = os.path.join(directory, file)
        if os.path.isfile(filename):
            with io.open(filename) as f:
                found = False
                for line in f:
                    if word in line:
                       found = not found
                       break
                if not found:
                   finalFiles += [file]
    return finalFiles
           

parser = argparse.ArgumentParser(description='The script to output files in which the substring is not found')
parser.add_argument("-d", "--dir", type=str,required=True, help='Input dir for searching')
parser.add_argument('-s',"--search", type=str,required=True, help='Searched substring in dir')
args = parser.parse_args()
if os.path.isdir(args.dir):
   result = unfind_substr(args.dir, args.search)
   for l in result:
       print(l)
print("done.")