Question

My knowledge of how file buffers work is fairly weak, so forgive the simple mindedness of this question. I have a piece of code in Python that waits for a file to appear, then reads it.

while 1:
    try:
        f = open('file.txt')
        f.close()
        print "Message received."
        break
    except:
        time.sleep(0.3)

Where file.txt is a file written by another program. However, I’ve a suspicion that Python is reading the file and then closing the handle before the file file.txt is completely written (that is, before I even call close() in the program that is writing the file). Should this even be possible?

If it is the case, is there a way I can detect (in the reading program listed above) whether or not the buffers have been flushed before I call f.close()?

Answer 1

Don’t use a while-loop for this purpose. There is a better way, though the details depend on your OS.

Linux has inotify. You can write a simple pyinotify script to watch the directory and react to IN_CLOSE_WRITE events (which occur only after the file has been closed).

OSX (FSEvents) and Windows have similar facilities.