I am looking for a string inside of a process, and it seems that the output of the check_output command depends on the screen size of the terminal I run the code in. 

Here I ran the code with a normal screen resolution:
>>> result = subprocess.check_output(['ps', 'aux']).decode('ascii', errors='ignore')
>>> 'app-id' in result
False
 
Then I zoom out to the point where I can barely read the text on the screen, and this is the output I get:
>>> result = subprocess.check_output(['ps', 'aux']).decode('ascii', errors='ignore')
>>> 'app-id' in result
True

Very strange, I tried with 3.8a and I did not get this issue.

Normally we use a pipe for stdin and stdout when we use check_output, so in this case, there is no relation with the size of the terminal. this is just a stream.

second point, you explain that you use python 3.5, could you try with 3.6 or 3.7 because 3.5 is in security mode and we won't work on this issue.

Thank you

This is due to the ps command itself. You'd have the same problem when piping to grep or redirecting output to a file. I don't know how it determines terminal size. I tried overriding stdin, stdout and stderr to pipes and calling setsid() in the forked child process to detach from the controlling terminal, but it still detected the terminal size. Anyway, the "ww" option of ps overrides this behavior.

I don’t think that is true. I tried grepping for what I need in a very small terminal and still got the correct result.

> On Oct 24, 2018, at 1:40 PM, Eryk Sun <report@bugs.python.org> wrote:
> 
> 
> Eryk Sun <eryksun@gmail.com> added the comment:
> 
> This is due to the ps command itself. You'd have the same problem when piping to grep or redirecting output to a file. I don't know how it determines terminal size. I tried overriding stdin, stdout and stderr to pipes and calling setsid() in the forked child process to detach from the controlling terminal, but it still detected the terminal size. Anyway, the "ww" option of ps overrides this behavior.
> 
> ----------
> nosy: +eryksun
> resolution:  -> third party
> stage:  -> resolved
> status: open -> closed
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue35060>
> _______________________________________

just one question, did you use this command in the REPL?

My script:

#!/usr/bin/env python
import pathlib
import subprocess

output = subprocess.check_output(['ps', 'aux'])
pathlib.Path('/tmp/ps_aux.txt').write_bytes(output)


When I execute the following script in the REPL, I get your issue but for me, it's normal because the REPL is running in a terminal with a limited size. 

And when I execute the same script like as a simple python script, I don't have your issue.

You are correct. It works as expected outside of the REPL.

> On Oct 24, 2018, at 4:34 PM, Stéphane Wirtel <report@bugs.python.org> wrote:
> 
> 
> Stéphane Wirtel <stephane@wirtel.be> added the comment:
> 
> My script:
> 
> #!/usr/bin/env python
> import pathlib
> import subprocess
> 
> output = subprocess.check_output(['ps', 'aux'])
> pathlib.Path('/tmp/ps_aux.txt').write_bytes(output)
> 
> 
> When I execute the following script in the REPL, I get your issue but for me, it's normal because the REPL is running in a terminal with a limited size. 
> 
> And when I execute the same script like as a simple python script, I don't have your issue.
> 
> ----------
> status: closed -> open
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue35060>
> _______________________________________

Here is the doc from ps with man.

> man ps

If ps cannot determine display width, as when output is redirected (piped) into a file or another command, the output width is undefined (it may be 80, unlimited, determined by the TERM variable, and so on).  The COLUMNS environment variable or --cols option may be used to exactly determine the width in this case.  The w or -w option may be also be used to adjust width.

-w     Wide output.  Use this option twice for unlimited width.


So for my part, in my terminal, the COLUMNS envvar is different in function of the size of my window, from 86 to 131 etc...

so, I think we can definitively close this issue.

Thank you,