Trying to create a CSV file with a file search using os.path

Question

I want to open the main folder containing all files (1), search though the files and only grab any .txt file with \"mtn\" in the title (2), print a the list of txt files (3)

Answer 1

You're opening the file multiple times in w+ mode (explained here in the documentation), which causes its contents to be truncated each time — so that's why you're only seeing the last one. You actually only need to open the file once, and then can write rows to it as needed.

Here's what I mean:

import csv
import fnmatch
import os

mtn_path = r'G:\somepath'
pattern = '*mtn*'
txt_file_csv_path = os.path.join(mtn_path, 'txt_file_list.csv')

with open(txt_file_csv_path, 'w+', newline='') as f:
    thewriter = csv.writer(f)
    # Write a header row.
    thewriter.writerow(['Filename', 'Path', ])
    num_files = 0

    for root, dirs, files in os.walk(mtn_path):
        for filename in files:
            if fnmatch.fnmatch(filename, pattern):
                num_files += 1
                thewriter.writerow((filename, os.path.join(root, filename)))
                print(filename)

print('The total number of mtn files found was ' + str(num_files))

Answer 2

The mode string 'w+' causes any existing contents to be truncated. Perhaps see further python open built-in function: difference between modes a, a+, w, w+, and r+?

You don't want to repeatedly open and close the same file anyway; just open it once outside the main loop, and then write whenever you have something more to write.

(Switching to 'a' instead of 'w+' would fix your code with a minimal change; but you then cause the operating system to do a fair amount of gymnastics to open the file, seek to the end, and close it again for every line you want to write.)