[Note] [One-line memo] If you add the -u option to Python, stdout and stderr become unbuffered. Useful when piped to a tee

The title is all about the content, but for the time being

python -c 'import time; print(1); time.sleep(1); print(2)

⇒ 1 is displayed, and after a while, 2 is displayed.

sh -c 'echo 1; sleep 1; echo 2'

⇒ 1 is displayed, and after a while, 2 is displayed.

python -c 'import time; print(1); time.sleep(1); print(2) | tee /dev/null

⇒ After a while, 1 and 2 are displayed at once

sh -c 'echo 1; sleep 1; echo 2' | tee /dev/null

⇒ 1 is displayed, and after a while, 2 is displayed.

Why does it behave differently only when piped in Python?

Python is smart, so if stdout and stderr are terminals, they will buffer the line buffer, otherwise they will buffer normally. (When outputting a lot, buffering is overwhelmingly faster) By the way, Python does it itself, so the stdbuf command can't change its behavior.

With the -u option, it becomes unbuffered.

python -u -c 'import time; print(1); time.sleep(1); print(2) | tee

⇒ 1 is displayed, and after a while, 2 is displayed.