How to hide output of subprocess in Python 2.7

309
votes

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?

5
pythonpython-2.7subprocessespeak
could you not just call with os.system then? not ideal but shouldnt print i dont think – Joran Beasley
@JoranBeasley: os.system() will print to the console unless you redirect the shell command – jdi
no, os.system('espeak '+ text) reproduces this behavior. – rypel
@ferkulat: I updated my answer to also show the os.system syntax. Though it is just for illustration. Stick with subprocess – jdi
Non 2.7 specific version: stackoverflow.com/questions/5495078/… which allows for the perfect subprocess.DEVNUL solution. – Ciro Santilli 新疆再教育营六四事件法轮功郝海东

5 Answers

480
votes

For python >= 3.3, Redirect the output to DEVNULL:

import os
import subprocess

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

It is effectively the same as running this shell command:

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

For python <3.3, including 2.7 use:

retcode = subprocess.call(['echo', 'foo'], 
    stdout=FNULL, 
    stderr=subprocess.STDOUT)
97
votes

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
32
votes

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)
30
votes

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)
-7
votes

Why not use commands.getoutput() instead?

import commands

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