How to hide output of subprocess in Python 2.7

Question

I'm using eSpeak on Ubuntu and have a Python 2.7 script that prints and speaks a message:

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

eSpeak produces the desired sounds, but clutters the shell with some errors (ALSA lib..., no socket connect) so i cannot easily read what was printed earlier. Exit code is 0.

Unfortunately there is no documented option to turn off its verbosity, so I'm looking for a way to only visually silence it and keep the open shell clean for further interaction.

How can I do this?

Answer 1

Redirect the output to DEVNULL:

import os
import subprocess

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

It is effectively the same as running this shell command:

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

Update: This answer applies to the original question relating to python 2.7. As of python >= 3.3 an official subprocess.DEVNULL symbol was added.

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

Answer 2

Here's a more portable version (just for fun, it is not necessary in your case):

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from subprocess import Popen, PIPE, STDOUT

try:
    from subprocess import DEVNULL # py3k
except ImportError:
    import os
    DEVNULL = open(os.devnull, 'wb')

text = u"René Descartes"
p = Popen(['espeak', '-b', '1'], stdin=PIPE, stdout=DEVNULL, stderr=STDOUT)
p.communicate(text.encode('utf-8'))
assert p.returncode == 0 # use appropriate for your program error handling here

Answer 3

Use subprocess.check_output (new in python 2.7). It will suppress stdout and raise an exception if the command fails. (It actually returns the contents of stdout, so you can use that later in your program if you want.) Example:

import subprocess
try:
    subprocess.check_output(['espeak', text])
except subprocess.CalledProcessError:
    # Do something

You can also suppress stderr with:

    subprocess.check_output(["espeak", text], stderr=subprocess.STDOUT)

For earlier than 2.7, use

import os
import subprocess
with open(os.devnull, 'w')  as FNULL:
    try:
        subprocess._check_call(['espeak', text], stdout=FNULL)
    except subprocess.CalledProcessError:
        # Do something

Here, you can suppress stderr with

        subprocess._check_call(['espeak', text], stdout=FNULL, stderr=FNULL)

Answer 4

As of Python3 you no longer need to open devnull and can call subprocess.DEVNULL.

Your code would be updated as such:

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

Answer 5

Why not use commands.getoutput() instead?

import commands

text = "Mario Balotelli" 
output = 'espeak "%s"' % text
print text
a = commands.getoutput(output)