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classification
Title: os.get_terminal_size() should check stdin as a fallback
Type: behavior Stage: patch review
Components: Extension Modules, Library (Lib) Versions: Python 3.10, Python 3.9, Python 3.8
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Arfrever, blueyed, denilsonsa, eryksun, grantjenks, vstinner, zbysz
Priority: normal Keywords: patch

Created on 2012-05-17 17:21 by Arfrever, last changed 2022-04-11 14:57 by admin.

Pull Requests
URL Status Linked Edit
PR 12697 open blueyed, 2019-04-05 11:25
Messages (7)
msg160988 - (view) Author: Arfrever Frehtes Taifersar Arahesis (Arfrever) * (Python triager) Date: 2012-05-17 17:21
$ stty size | cat
46 157
$ python3.3 -c 'import os; print(os.get_terminal_size())' | cat
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OSError: [Errno 22] Invalid argument

Redirection to `less` are often used.

A proposed patch was attached by Victor Stinner in issue #13609.
msg222266 - (view) Author: Mark Lawrence (BreamoreBoy) * Date: 2014-07-04 07:28
#13609 is closed fixed so can this also be closed?  I've tried to reproduce this on Windows with the help of unxutils but it didn't want to know, sorry :(
msg222272 - (view) Author: Arfrever Frehtes Taifersar Arahesis (Arfrever) * (Python triager) Date: 2014-07-04 09:02
This bug is still reproducible in Python 3.4 and 3.5.
msg222527 - (view) Author: Denilson Figueiredo de Sá (denilsonsa) Date: 2014-07-07 22:10
FYI, "tput" tool can find out the dimensions even when both stdin and stdout are redirected. It can't, however, if all stdin, stdout and stderr are redirected. Python should probably implement a similar logic.

$ echo | stty size
stty: standard input: Inappropriate ioctl for device
$ echo | tput cols | cat
223
$ echo | tput cols 2>&1 | cat 
80

(tested under Linux)
msg323836 - (view) Author: Grant Jenks (grantjenks) * Date: 2018-08-21 17:19
I asked on the ncurses maintainers email list about their logic and was pointed to tty_settings.c which checks:

1. stderr
2. stdout
3. stdin
4. open('/dev/tty', 'r+')

I don't know a cross-platform way to check #4 but I think #1-3 are a reasonable change to shutil.get_terminal_size().

The current logic checks only stdout. I'd like to amend that to try stderr, stdout, and stdin after checking the COLUMNS and LINES env vars. So the new logic would be:

1. Check COLUMNS and LINES env vars (for overrides)
2. Check os.get_terminal_size(stderr)
3. Check os.get_terminal_size(stdout)
4. Check os.get_terminal_size(stdin)
msg323847 - (view) Author: Eryk Sun (eryksun) * (Python triager) Date: 2018-08-21 22:16
The Windows implementation shouldn't map file-descriptor values 0, 1, and 2 to the process standard handles. fileno(stdout) may not even be 1 in some cases. It should use `handle = _get_osfhandle(fd)`, which is more generally correct and not limited to hard-coded defaults. 

Regarding this issue, the docs should clarify that the Windows console's input buffer cannot be used to get the screen buffer size. Typically the input buffer is STDIN_FILENO (0) or opened via  "CONIN$" or "CON" (read mode). Thus there is no point to checking stdin in Windows since it will always fail.

I agree that the default behavior should be extended to check a platform-dependent tty/console device. In Windows this is `fd = _open("CONOUT$", _O_RDWR)`.
msg339495 - (view) Author: daniel hahler (blueyed) * Date: 2019-04-05 11:52
Created a PR at https://github.com/python/cpython/pull/12697.

It prefers stdin and stderr over stdout.

I think stdin is most likely connected to a terminal, and wondered why ncurses uses stderr/stdout first, and only then stdin.
stdin handling was added there in https://github.com/mirror/ncurses/commit/aa70bf3c#diff-10ad6ea20599ac9258757354665b80cbR1295, and it looks just like an oversight maybe - it is also not that critical in C I guess.
History
Date User Action Args
2022-04-11 14:57:30adminsetgithub: 59046
2021-03-06 15:30:25eryksunsetcomponents: + Extension Modules, Library (Lib)
versions: + Python 3.9, Python 3.10, - Python 3.4, Python 3.5, Python 3.6, Python 3.7
2019-04-05 11:52:14blueyedsetnosy: + blueyed
messages: + msg339495
2019-04-05 11:25:01blueyedsetkeywords: + patch
stage: patch review
pull_requests: + pull_request12622
2018-08-21 22:16:21eryksunsetnosy: + eryksun
messages: + msg323847
2018-08-21 20:01:01BreamoreBoysetnosy: - BreamoreBoy
2018-08-21 17:19:30grantjenkssetnosy: + grantjenks

messages: + msg323836
versions: + Python 3.6, Python 3.7, Python 3.8
2014-07-07 22:10:50denilsonsasetmessages: + msg222527
2014-07-04 09:02:17Arfreversetmessages: + msg222272
2014-07-04 07:28:52BreamoreBoysetversions: + Python 3.4, Python 3.5, - Python 3.3
nosy: + BreamoreBoy

messages: + msg222266

type: behavior
2012-05-17 17:21:13Arfrevercreate