Failing to iterate over captured StdOut

[tester_V]

Greetings!
I’m using a subprocess to run and capture an output of the “ARP- A” command to a list.
I’d like to iterate and filter some of the IPs from the captured list but I’m failing with no errors.
If I capture the same output to a file I have no problem with filtering IPs I want.
Code:

from pathlib import Path
import subprocess
import re

kk = []        
output = subprocess.run(
        ["arp", "-a"],
        #encoding="utf-8",
        capture_output=True,
        creationflags=subprocess.CREATE_NO_WINDOW,   # Notice this is a function argument, not variable assignment
    )
kk.append(output.stdout.strip())

for el in kk :
    el=el.strip()
    if "192.168.1" in el :
        cell = re.split('\s+', el)
       # and so on...

I understand stdout I'm capturing is in a 'wrong' format to do line by line search. I'm not sure how to get around this problem.
Thank you!

[deanhystad]

output.stdout is bytes. Use decode to convert to a str.

import subprocess

output = subprocess.run(
        ["arp", "-a"],
        capture_output=True,
        creationflags=subprocess.CREATE_NO_WINDOW,
)
for i, line in enumerate(output.stdout.decode('utf-8').splitlines()):
    print(i, line)

The "encoding" argument in the run() command is for input, not output. Your command doesn't use input, so there is no need to provide an encoder.

The reason things work when you write output to a file is that reading from a text file invokes a decoder to convert the bytes in the file to python strings.

[tester_V]

Great! I learned something new.
I removed 'enumerate', I do not need it, and it works great!
Thank you! You guys are awesome!

import subprocess
 
output = subprocess.run(
        ["arp", "-a"],
        capture_output=True,
        creationflags=subprocess.CREATE_NO_WINDOW,
)
aa = (output.stdout.decode('utf-8').splitlines())
for i in aa :
    if "192.168.1" in i :
        print(f" Found =>  {i}")

[Gribouillis]

If you add an encoding argument in run(), I think it may output a str instead of a bytes

subprocess. run(..., encoding='utf8')

[deanhystad]

Gribouillis is correct (as usual). This works fine.

import subprocess

output = subprocess.run(
    ["arp", "-a"],
    encoding="utf-8",
    capture_output=True,
    creationflags=subprocess.CREATE_NO_WINDOW,
)
for i, line in enumerate(output.stdout.splitlines()):
    print(i, line)

Somehow I missed this in the documentation:

If encoding or errors are specified, or text is true, file objects for stdin, stdout and stderr are opened in text mode using the specified encoding and errors or the io.TextIOWrapper default. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.

And this:

stdout¶
Captured stdout from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stdout was not captured.

Not a good day for me.