Why a new NamedTemporaryFile object has a path, but a file is not available?

Question

I am doing a 30 Days of Python course on Udemy. In Day 16 part 2 I got stuck with creating edit_data (in my code: edytuj_dane) function. I would like to store some values to a temporary file (NamedTemporaryFile object) using DictWriter and then move the content to a CSV file (dane.csv) that should by updated by each command of the function.

I got confused as there is an error that I can't access the temp file created by NamedTemporaryFile object, whereas checking the path it seems that it is not available at all (also checked if it's hidden). Could you please check and let me know if you have any ideas how to fix the error?

The dane.csv file content is as below:

id,name,email,amount,sent,date

1,2,3,4,5,6

And the executed code is below:

def edycja_danych(edit_id = None, email = None, sent = None, amount = None):
    nazwa_pliku = 'data.csv'
    plik_tymczasowy = NamedTemporaryFile(delete=True, mode ='w') 

    with open(nazwa_pliku, 'r') as csvfile, plik_tymczasowy:
        reader = csv.DictReader(csvfile)
        tytuly = ['id','name','email', 'amount', 'sent', 'date']
        writer = csv.DictWriter(plik_tymczasowy, fieldnames = tytuly)
    
        writer.writeheader() 
        
        for row in reader:
            writer.writerow(row)
            shutil.copyfile(plik_tymczasowy.name, nazwa_pliku)

edycja_danych(email='qwerty@gmail.com', amount = 90, sent = '')

Actually the code execution ends up with following error:

PermissionError: [Errno 13] Permission denied: 'C:\Users\Marek\AppData\Local\Temp\tmpjr622sbn'

Whereas, it should (I think so at least) end up with no error and the file being updated.

that and indent issues that make the file go "out of scope" of a with block and ends up deleted. — Jean-François Fabre, Apr 02 '19 at 18:49
don't use temporary file for this (unless data is big). Use `io.StringIO` to create a fake file to pass to csv. — Jean-François Fabre, Apr 02 '19 at 18:50
@Jean-FrançoisFabre There's nothing wrong with using `NamedTemporaryFile` here, at least assuming you use `os.rename` instead of `shutil.copyfile` to create the target file *atomically*. — chepner, Apr 02 '19 at 18:54
You appear to be trying to copying your temp file into your input file, and you are trying to do so after writing every row, rather than after all the writes are complete. — chepner, Apr 02 '19 at 19:00
@chepner it's better to rename, but it works only if you're on the same filesystem. `shutil.move` is preferred in the general case — Jean-François Fabre, Apr 02 '19 at 19:01
it's a duplicate because you're trying to access the file when it's not closed yet. — Jean-François Fabre, Apr 02 '19 at 19:03

Why a new NamedTemporaryFile object has a path, but a file is not available?

0 Answers0