Suppressing

Here is how to suppress output, in order of decreasing levels of cleanliness. They assume you are on Python 3.

1. You can redirect to the special subprocess.DEVNULL target.

import subprocess

# To redirect stdout (only):
subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.DEVNULL
)

# to redirect stderr to /dev/null as well:
subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.DEVNULL,
    stderr = subprocess.DEVNULL
)

# Alternatively, you can merge stderr and stdout streams and redirect
# the one stream to /dev/null
subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.DEVNULL,
    stderr = subprocess.STDOUT
)

2. If you want a fully manual method, can redirect to /dev/null by opening the file handle yourself. Everything else would be identical to method #1.

import os
import subprocess

with open(os.devnull, 'w') as devnull:
    subprocess.run(
        ['ls', '-l'],
        stdout = devnull
    )

Capturing

Here is how to capture output (to use later or parse), in order of decreasing levels of cleanliness. They assume you are on Python 3.

NOTE: The below examples use universal_newlines=True (Python <= 3.6).

• This causes the STDOUT and STDERR to be captured as str instead of bytes.
  • Omit universal_newlines=True to get bytes data
• Python >= 3.7 accepts text=True as a short form for universal_newlines=True

1. If you simply want to capture both STDOUT and STDERR independently, AND you are on Python >= 3.7, use capture_output=True.

import subprocess

result = subprocess.run(
    ['ls', '-l'],
    capture_output = True, # Python >= 3.7 only
    text = True # Python >= 3.7 only
)
print(result.stdout)
print(result.stderr)

2. You can use subprocess.PIPE to capture STDOUT and STDERR independently. This works on any version of Python that supports subprocess.run.

import subprocess

result = subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.PIPE,
    universal_newlines = True # Python >= 3.7 also accepts "text=True"
)
print(result.stdout)

# To also capture stderr...
result = subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.PIPE,
    stderr = subprocess.PIPE,
    universal_newlines = True # Python >= 3.7 also accepts "text=True"
)
print(result.stdout)
print(result.stderr)

# To mix stdout and stderr into a single string
result = subprocess.run(
    ['ls', '-l'],
    stdout = subprocess.PIPE,
    stderr = subprocess.STDOUT,
    universal_newlines = True # Python >= 3.7 also accepts "text=True"
)
print(result.stdout)

You’ll need to use the stdout and/or stderr arguments. https://docs.python.org/3/library/subprocess.html#subprocess.run

Edit: link to #subprocess.run

If you have Python version 2.7 or later, you can use subprocess.check_output which basically does exactly what you want (it returns standard output as a string).

A simple example (Linux version; see the note):

import subprocess

print subprocess.check_output(["ping", "-c", "1", "8.8.8.8"])

Note that the ping command is using the Linux notation (-c for count). If you try this on Windows, remember to change it to -n for the same result.

As commented below, you can find a more detailed explanation in this other answer.

In Python 2.7 or Python 3

Instead of making a Popen object directly, you can use the subprocess.check_output() function to store output of a command in a string:

from subprocess import check_output
out = check_output(["ntpq", "-p"])

In Python 2.4-2.6

Use the communicate method.

import subprocess
p = subprocess.Popen(["ntpq", "-p"], stdout=subprocess.PIPE)
out, err = p.communicate()

out is what you want.

Important note about the other answers

Note how I passed in the command. The "ntpq -p" example brings up another matter. Since Popen does not invoke the shell, you would use a list of the command and options—["ntpq", "-p"].

Use subprocess.Popen:

import subprocess
process = subprocess.Popen(['ls', '-a'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = process.communicate()
print(out)

Note that communicate blocks until the process terminates. You could use process.stdout.readline() if you need the output before it terminates. For more information see the documentation.