# Prompt for three values: input file, output file, search string.
# Search for the string in the input file, write results to the
# output file

import sys
def process_file(i_file, o_file, a_str):
    ''' if the a_str is in a line of i_file, add stars
        to the a_str in line, write it out with the
        line number to o_file'''
    line_count_int = 1
    for line_str in i_file:
        if a_str in line_str:
            new_line_str = line_str.replace(a_str, '***'+a_str)
            print('Line {}: {}'.format(line_count_int, new_line_str),\
                  file=o_file)
        line_count_int += 1

try:
    in_file_str = input("File to search:")
    in_file = open(in_file_str, 'r', encoding='utf_8')
except IOError:
    print('{} is a bad file name'.format(in_file_str))
    sys.exit()

out_file_str = input("File to write results to:")
out_file = open(out_file_str, 'w')
search_str = input("Search for what string:")
process_file(in_file, out_file, search_str)
in_file.close()
out_file.close()