What mode should i open the file to write into a *.msh file

[Dhanya]

Hi,
I am trying to update a *.msh file by finding a 'find_word' and replace it with rep_word'.
I wrote a program to read an input csv file where I will be giving these fields. - file_type(values input are msh,mshs), folder_path(path where files are to be searched for the word and replaced), sub_directory(ignore as of now), find_word(the workd which needs to be searched), rep_word(the word to be replaced).

import os
import re
import csv

"""Replace a word in the file with the replace word and writes into the file"""
def check_and_replace(file, find_word, rep_word):
        rfile = open(file, 'rt')
        string = rfile.read()
        rfile.close()
        string = re.sub(find_word, rep_word, string)
        wfile = open(file, 'wt')
        wfile.write(string)
        wfile.close()

"""Reads the input test file and gets the values for file type, folderpath, subdirectory value, find word and replace word"""
"""file_type will have values like msh or mshs"""
"""folder_path will have value of the folder where replace is done"""
"""find word is the search word and rep_word is the word to be replaced"""
with open('test csv.csv', 'r') as csv_file:
    next(csv_file)
    csv_reader = csv.reader(csv_file)
    for line in csv_reader:
        file_type = line[0]
        folder_path = line[1]
        sub_directory = line[2]
        find_word = line[3]
        rep_word = line[4]
        for path, subdirs, files in os.walk(folder_path):
            for file in files:
                if file.endswith(file_type):
                    new_file_name = os.path.join(path, file)
                    check_and_replace(new_file_name, find_word, rep_word)

sample msh file
input file