How to write datas into a file?

[Krszt]

I have program, which looks for every files starting with mli_value_IHAR_. I want these files' special date ID into a file (every date into a new line). Here is the code that I wrote. My problem is that the final txt file contains only the last element's date. Where do I make a mistake?

for path, subdirs, files in os.walk(r'./'):
    for filename in files:
        if filename.startswith("mli_value_IHAR_"):
            f = os.path.join(path, filename)
            print(f)
            date = (f[-12:-4])
            print(date)
            with open('test.txt', 'w') as data_file:
                data_file.write(str('%s\n' % date))

[buran]

you open and close the test.txt every time you write in it. However the mode is 'w'. i.e. if the file exists it is replaced by new file. that is why you get just the last entry. use mode 'a' or you can open the file at the beginning and close it after you end iterating over the files. The drawback is you will get empty file if no file match the condition

[Krszt]

you open and close the test.txt every time you write in it. However the mode is 'w'. i.e. if the file exists it is replaced by new file. that is why you get just the last entry. use mode 'a' or you can open the file at the beginning and close it after you end iterating over the files. The drawback is you will get empty file if no file match the condition

Than you very much, it solved my problem!