How Can I Suppress Subprocess Output in Python?

Suppression of Subprocess Output

When invoking external programs using Python's subprocess library, their console output can become a nuisance, especially for verbose applications like eSpeak. This issue arises as eSpeak emits diagnostic messages alongside the intended audio, cluttering the shell and hindering subsequent interactions.

To address this problem, we can employ a technique known as output redirection. In Python >= 3.3, the DEVNULL device can be used to redirect both standard output and error streams to a null destination, effectively silencing them:

import os
import subprocess

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

For Python < 3.3, including 2.7, the following approach can be used:

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

This method is equivalent to running the following shell command:

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

This technique ensures that the unwanted output from eSpeak is suppressed, leaving the shell clean and ready for further user interaction.
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