How to use subprocess without Try-Catch?

Question

**Can someone answer my question under the only answer? **

I want to use subprocess and be able to read its output, so I used:

subprocess.check_output

But this wasn't enough for me, I wanted to hide writing to stderror so I added:

stderr=subprocess.DEVNULL

Which wasn't helpful as some commands now have the following output:

raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['snmpwalk', '-t', '1', '-r', '1', '-v', '3', '-c', 'public', '31.208.215.122', '1.3.6.1.2.1.1.2.0']' returned non-zero exit status 1.

How can I fix this without try-catch (I don't want to harm performance as I am calling this code thousands of times)?

Only you can know which encoding to use for your snmpwalk program. encoding="utf-8" is a safe choice for UNIX programs, in general. — AKX
– AKX, Commented Mar 7, 2022 at 14:02

CIsForCookies · Accepted Answer · 2022-03-07 16:14:24Z

1

subprocess.run is your friend

subprocess.check_output will raise Exception upon failure. .run won't (unless given check=True)

Try something like:

In [1]: import subprocess

In [2]: proc = subprocess.run("echo bla", shell=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)

In [3]: print(proc.stdout.decode())
bla

edited Mar 7, 2022 at 16:14

answered Mar 7, 2022 at 13:24

CIsForCookies

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6 Comments

CIsForCookies Over a year ago

It does, if you use stdout=subprocess.PIPE and then read the return object's stdout. Read the doc

chepner Over a year ago

It's your responsibility to tell subprocess.run which encoding to use, or to know how to decode it once you get the raw byte stream from the subprocess. You can use text=True and see if the default encoding works for you, though.

chepner Over a year ago

Use the encoding argument if UTF-8 isn't already the default. Please see the documentation for subprocess.run.

Dan Over a year ago

@chepner encoding=encodings.utf_8 doesn't work

Ted Klein Bergman Over a year ago

@Dan "Doesn't work" will help people understand what the problem is. You must explain exactly what doesn't work. And why are you doing encoding=encodings.utf_8? Nobody told you to do that. They explicitly wrote encoding="utf-8".

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