bpo-14841: shutil.get_terminal_size: use stdin/stderr also by blueyed · Pull Request #12697 · python/cpython

blueyed · 2019-04-05T11:25:00Z

stdout might be a pipe, e.g. less, and then stdin or stderr should be
used to query the terminal for its size.

This patch prefers stdin, since that is most likely connected to a
terminal.

https://bugs.python.org/issue14841

stdout might be a pipe, e.g. `less`, and then stdin or stderr should be used to query the terminal for its size. This patch prefers stdin, since that is most likely connected to a terminal.

This uses an improved version of `shutil.get_terminal_width` [1], and also improves the code for before Python 3.3. 1: https://bugs.python.org/issue14841, python/cpython#12697

denilsonsa · 2019-04-05T22:47:14Z

This patch prefers stdin, since that is most likely connected to a terminal.

My gut feeling says stderr is more likely to be a terminal than stdin; but it really doesn't matter, because I see all three are being tried in the code.

blueyed · 2019-04-06T01:25:18Z

My gut feeling says stderr is more likely to be a terminal than stdin

Why is that?
I would assume that stdin usually is connected / open for input, while stderr might also be redirected - less likely then stdout, but still.

This uses an improved version of `shutil.get_terminal_width` [1], and also improves the code for before Python 3.3. 1: https://bugs.python.org/issue14841, python/cpython#12697

This uses an improved version of `shutil.get_terminal_width`, mainly to look at stdin, stderr, and stdout. Ref: https://bugs.python.org/issue14841 Ref: python/cpython#12697 Rejected/stalled in pylib: pytest-dev/py#219 Suggested to move into pytest in pytest-dev#5056.

blueyed · 2019-11-01T13:31:45Z

Note that os.get_terminal_size might return (0, 0) also, which should be handled (blueyed/pytest#43).
That appears to be an existing issue already, and this PR (or the issue) appears to get no traction, so I will not update it for now - but the linked PR has a fix (I've used the function from this PR there).

vstinner · 2021-03-08T18:29:42Z

Lib/shutil.py

+            for check in [sys.__stdin__, sys.__stderr__, sys.__stdout__]:
+                try:
+                    size = os_get_terminal_size(check.fileno())
+                except (AttributeError, ValueError, OSError):
+                    # fd is None, closed, detached, or not a terminal.
+                    continue
+                else:
+                    break


Suggested change

for check in [sys.__stdin__, sys.__stderr__, sys.__stdout__]:

try:

size = os_get_terminal_size(check.fileno())

except (AttributeError, ValueError, OSError):

# fd is None, closed, detached, or not a terminal.

continue

else:

break

for stream in (sys.__stdin__, sys.__stderr__, sys.__stdout__):

try:

size = os_get_terminal_size(stream.fileno())

break

except (AttributeError, ValueError, OSError):

# stream is None, closed, detached, or not a terminal.

pass

vstinner · 2021-03-08T18:30:56Z

Lib/test/test_shutil.py

+                actual = shutil.get_terminal_size()
+                self.assertEqual(expected, actual)
+
+            # Falls back to stderr.


The test is decorated with @unittest.skipUnless(os.isatty(sys.__stdout__.fileno()), "not on tty"). What if stderr is not a TTY?

vstinner · 2021-03-08T18:31:19Z

Lib/test/test_shutil.py


-            # sys.__stdout__ has no fileno()
-            with support.swap_attr(sys, '__stdout__', None):
+            # stdin/stderr/stdout have no fileno().


Suggested change

# stdin/stderr/stdout have no fileno().

# stdin/stderr/stdout have no fileno() method

vstinner · 2021-03-08T18:33:42Z

Lib/shutil.py

-    the terminal connected to sys.__stdout__ is queried
-    by invoking os.get_terminal_size.
+    the terminal connected to sys.__stdin__, sys.__stderr__, or sys.__stdout__
+    is queried by invoking os.get_terminal_size.


I would prefer to trust ncurses developers and use the order that they suggested:
https://bugs.python.org/issue14841#msg323836

Please add a comment below on the loop iterating on streams, to add a reference to bpo-14841 to explain why in which order streams are tested.

python-cla-bot · 2025-04-06T14:36:34Z

The following commit authors need to sign the Contributor License Agreement:

git@thequod.de

github-actions · 2025-09-21T06:03:50Z

This PR is stale because it has been open for 30 days with no activity.

vstinner · 2025-09-22T12:50:32Z

This PR is idle for 4 years.

github-actions · 2026-02-01T12:05:42Z

This PR is stale because it has been open for 30 days with no activity.

bpo-14841: shutil.get_terminal_size: use stdin/stderr also

cd96f2d

stdout might be a pipe, e.g. `less`, and then stdin or stderr should be used to query the terminal for its size. This patch prefers stdin, since that is most likely connected to a terminal.

bedevere-bot added the awaiting review label Apr 5, 2019

the-knights-who-say-ni added the CLA signed label Apr 5, 2019

blueyed mentioned this pull request Apr 5, 2019

Display message from reprcrash in short test summary pytest-dev/pytest#5013

Merged

blueyed added 3 commits April 5, 2019 14:02

tests

c614adc

fixup! bpo-14841: shutil.get_terminal_size: use stdin/stderr also

364a192

check for os.get_terminal_size explicitly

5baa778

blueyed mentioned this pull request Apr 5, 2019

Fix _getdimensions for when stdout is redirected pytest-dev/py#219

Closed

blueyed mentioned this pull request Nov 1, 2019

Adopt/inherit TerminalWriter from py.io for better width blueyed/pytest#41

Merged

vstinner reviewed Mar 8, 2021

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bpo-14841: shutil.get_terminal_size: use stdin/stderr also#12697

bpo-14841: shutil.get_terminal_size: use stdin/stderr also#12697
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blueyed commented Apr 5, 2019 •

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