search_in_files.py

import os
import csv

FILE_EXT = '.dat'
SEARCH_TERMS = ('one line to search for \n', 'another line to search for\n')


file_list = [f for f in os.listdir() if f.endswith(FILE_EXT)]

output = [['file name', 'search term 1 exists', 'search term 2 exists']]
for fname in sorted(file_list):
    with open(fname) as f:
        lines = f.readlines()
    
    output.append([filename] + [term in lines for term in SEARCH_TERMS])

with open('results.csv', 'w') as f:
    writer = csv.writer(f)
    writer.writerows(output)