Redirect log to file before process finished [duplicate]

Question

test.py (work):

import time _, a, b = [1, 2, 3] print a print b

run the code: python test.py > test.log

you will get the log in test.log

test.py (not work):

import time _, a, b = [1, 2, 3] print a print b while True: time.sleep(5)

But this one you get None in the log.

How do I get log before the program finished, without the python log module(just use the redirect '>')?

Lookup "flush output". I marked your question as a duplicate of another one. Though it said "screen" and not file, it's actually the same thing from your program's perspective. — spectras
– spectras, Commented Jun 15, 2016 at 5:40
the fifth answer is worked for file,but not accepted in that question. — Levi
– Levi, Commented Jun 15, 2016 at 5:48

Bi Rico · Accepted Answer · 2016-06-15 05:40:51Z

Python buffers stdout by default so the log gets written to disk in chunks. You can turn off the buffering a few different ways, here are two. You can use the -u option when you call the script, ie:

python -u test.py

You can use the enviornment varialbe PYTHONUNBUFFERED:

export PYTHONUNBUFFERED=true python test.py

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