New submission from Alexey Izbyshev <[email protected]>:
When redirecting, subprocess attempts to achieve the following state: each fd
to be redirected to is less than or equal to the fd it is redirected from,
which is necessary because redirection occurs in the ascending order of
destination descriptors. It fails to do so if a low fd (< 2) is redirected to
stderr and another low fd is closed, which may lead to an incorrect
redirection, for example:
$ cat test.py
import os
import subprocess
import sys
os.close(0)
subprocess.call([sys.executable, '-c',
'import sys; print("Hello", file=sys.stderr)'],
stdin=2,
stderr=1)
$ python3 test.py 2>/dev/null
$ python3 test.py >/dev/null
Hello
Expected behavior:
$ python3 test.py >/dev/null
$ python3 test.py 2>/dev/null
Hello
----------
components: Extension Modules, Library (Lib)
messages: 312181
nosy: gregory.p.smith, izbyshev
priority: normal
severity: normal
status: open
title: subprocess may incorrectly redirect a low fd to stderr if another low fd
is closed
type: behavior
versions: Python 3.6, Python 3.7
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Python tracker <[email protected]>
<https://bugs.python.org/issue32844>
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