python 2.7 flush to file doesn't work until program terminates

Asked Oct 12 '17 at 23:24

Active Oct 13 '17 at 00:29

Viewed 79 times

I'm trying to flush all of std out to a python file via:

sys.stdout = open('myfile.txt', 'w')
print("Starting work")
sys.stdout.flush()
whole bunch of stuff with prints and sys.stdout.flush() mixed in
print("ending work")
sys.stdout.flush()

Unfortunately, nothing prints until the script terminates. The file size remains 0 kb. I am doing this on a windows machine if that helps with python 2.7

Thank you!

edited Oct 13 '17 at 00:29

Barmar

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asked Oct 12 '17 at 23:24

user1357015

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Can you do `sys.stdout = open('file', 'w', 0)` to stop any buffering? – Stuart Buckingham Oct 12 '17 at 23:37
Flushing isn't enough, you need to`close` the file. – Mark Ransom Oct 13 '17 at 00:02
@MarkRansom: But how do I close the file while the program is still running? That wouldn't work.... – user1357015 Oct 13 '17 at 00:23
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@MarkRansom Why isn't flushing enough? What do you think it does? – Barmar Oct 13 '17 at 00:25
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According to https://stackoverflow.com/questions/230751/how-to-flush-output-of-python-print what you've written should work. – Barmar Oct 13 '17 at 00:29
@Barmar: and yet it does not. – user1357015 Oct 13 '17 at 00:35
Does it work if you do `sys.stdout.write()` instead of `print`? – Barmar Oct 13 '17 at 00:39
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@Barmar flushing makes sure all the data gets to the OS, but it doesn't guarantee the OS will finish writing it to disk. Screen output is different than file output. – Mark Ransom Oct 13 '17 at 01:59
@MarkRansom We're not talking about writing to disk. The question says that the OS says that the file size is 0 bytes. If it gets to the OS, it should update the file size. – Barmar Oct 13 '17 at 15:42
@MarkRansom To get it to the disk, closing isn't enough -- you have to `fsync()`. – Barmar Oct 13 '17 at 15:42

python 2.7 flush to file doesn't work until program terminates

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