How Can I Suppress Unwanted Output from Subprocesses in Python?

Suppression of Subprocess Output in Python

In Python, subprocesses can be employed to execute various system commands. While such subprocesses may provide necessary functionality, their inherent verbosity can clutter output and hamper readability. In particular, consider the example provided by the user:

import subprocess
text = 'Hello World.'
print text
subprocess.call(['espeak', text])

In this instance, eSpeak generates the desired audio output but also produces unwanted error messages. This cluttering of the shell can make it challenging to access or interpret printed text. Unfortunately, there is no documented option to disable eSpeak's verbosity.

To address this issue, Python offers a convenient solution for suppressing subprocess output, allowing users to maintain a clean and clutter-free shell:

Solution:

Redirect the subprocess output to DEVNULL using the following code for Python >= 3.3:

import os
import subprocess

retcode = subprocess.call(['echo', 'foo'], 
    stdout=subprocess.DEVNULL,
    stderr=subprocess.STDOUT)

For Python versions below 3.3, including 2.7, utilize the code below:

FNULL = open(os.devnull, 'w')
retcode = subprocess.call(['echo', 'foo'], 
    stdout=FNULL, 
    stderr=subprocess.STDOUT)

This technique effectively mirrors the following shell command:

retcode = os.system("echo 'foo' > /dev/null")

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