Occasional IOError writing to file

Question

I am running the following code very often to write to files from Python using the following:

def function():
    file = os.path.join(os.path.dirname(os.path.abspath(__file__)), '../../my_file')
    fifo = open(file, 'w')
    if (os.path.isfile(file) and os.access(file, os.W_OK)):
        fifo.write("stuff")
        fifo.close()
    else:
        time.sleep(1)
        function()

Unfortunately, I get the following error (not all the time):

IOError: [Errno 2] No such file or directory

This is self-explanatory, but I do not understand then why all the precautions do not work, like isfile or access..W_OK ? How do I avoid having this issue?

Also, the slower the machine, the less often the error is encountered.

Where are you getting the error? Note that you open the file before checking for access. — Koterpillar, Jan 12 '16 at 10:37
Are there other processes that might delete the file or move the directories around? — Koterpillar, Jan 12 '16 at 10:41
@Koterpillar there is another process that deletes the file, but only after reading it — Boris Mocialov, Jan 12 '16 at 10:42
Not really an answer to the original question, but try writing to another file and renaming it to `my_file` when you're done. Renaming is atomic and won't cause race conditions. — Koterpillar, Jan 12 '16 at 10:44
your check and write are not atomic so it's only normal to fail sometimes if you have another process that deletes that file — user3012759, Jan 12 '16 at 10:44
You both make sense.. havent thought of that classical issue — Boris Mocialov, Jan 12 '16 at 10:45

score 0 · Accepted Answer · edited May 23 '17 at 12:23

See also "LBYL vs EAFP in Java?":

Instead of checking if the action is ok (LBYL), you should do an EAFP approach. Just do what you want to do and check if it has worked correctly.

Besides, better don't call function() recursively, it might lead to a stack overflow if the error persists.

Better do

def function():
    file = os.path.join(os.path.dirname(os.path.abspath(__file__)), '../../my_file')
    while True:
        try:
            with open(file, 'w') as file: # automatically closes...
                file.write("some stuff")
        except IOError, e:
            time.sleep(1)
            continue
        break # the while loop

your solution suits me best as it requires minimal changes to the existing code. Thank you — Boris Mocialov, Jan 12 '16 at 11:21

Occasional IOError writing to file

1 Answers1