What should go to stdout/stderr and why Python logging write everything to stderr?

[Weatherby,Gerard]

If sys.stdout is a tty, it typically flushes on newline. e. g.

!/usr/bin/env python3
import time
import sys
print("No flush",end='',file=sys.stdout)
time.sleep(2)
print("flushed",file=sys.stdout)
time.sleep(5)

will print the “flushed” 5 seconds before the script ends

From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of Eryk Sun <eryksun at gmail.com>
Date: Tuesday, January 3, 2023 at 1:33 PM
To: c.buhtz at posteo.jp <c.buhtz at posteo.jp>
Cc: python-list at python.org <python-list at python.org>
Subject: Re: What should go to stdout/stderr and why Python logging write everything to stderr?
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On 1/3/23, c.buhtz at posteo.jp <c.buhtz at posteo.jp> wrote:
>
> If the user request the usage info via "-h" it goes to stdout.

The standard file for application output is sys.stdout. Note that
sys.stdout may be buffered, particularly if it isn't a tty. When a
file is buffered, writes are aggregated and only written to the OS
file when the buffer fills up or is manually flushed.

> Why does logging behave different? DEBUG and INFO imho should go to
> stdout not stderr.

The standard file for error messages and other diagnostic information
is sys.stderr. This file should never be buffered.
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