Is shutil.get_terminal_size useless?

Wildman best_lay at yahoo.com
Mon Jan 30 00:59:19 EST 2017


On Sat, 28 Jan 2017 19:03:42 +1100, Steve D'Aprano wrote:

> shutil.get_terminal_size returns the wrong values when you pipe your output
> to another process, even it you do so in a terminal. Consider this script:
> 
> 
> import os
> import shutil
> print('shutil:', shutil.get_terminal_size(fallback=(999, 999)))
> print('os:', os.get_terminal_size(0))
> 
> 
> That uses two different methods to get the terminal size. If I run that in a
> terminal in the normal way, it works fine, returning the correct size for
> my terminal:
> 
> 
> [steve at ando ~]$ python3.5 test_gts.py
> shutil: os.terminal_size(columns=116, lines=29)
> os: os.terminal_size(columns=116, lines=29)
> 
> 
> But if I pipe the output to something else, the shutil version fails to
> determine the correct terminal size, and falls back on the default:
> 
> 
> [steve at ando ~]$ python3.5 test_gts.py | cat
> shutil: os.terminal_size(columns=999, lines=999)
> os: os.terminal_size(columns=116, lines=29)
> 
> 
> while the os version gives the correct result.
> 
> Is shutil.get_terminal_size useless? When, if ever, should I use it in
> preference to the os version? If the shutil version is broken, can it be
> fixed?
> 
> 
> Thanks to Bernardas Ališauskas:
> 
> http://granitosaurus.rocks/getting-terminal-size.html

I can suggest a third approach to try but I have not tried
piping it.  YMMV.

import fcntl
import os
import struct
import termios

tty = os.open(os.ctermid(), os.O_RDONLY)
ts = struct.unpack("hh", fcntl.ioctl(tty, termios.TIOCGWINSZ, "1234"))
os.close(tty)
columns = ts[1]
rows = ts[0]
print(str(columns) + "x" + str(rows))

-- 
<Wildman> GNU/Linux user #557453
The cow died so I don't need your bull!


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