How to suppress console output in Python?

Question

I\'m using Pygame/SDL\'s joystick module to get input from a gamepad. Every time I call its get_hat() method it prints to the console. This is problematic since

Answer 1

If you are on a Debian or Ubuntu machine you can just simply recompile pygame without the messages.

cd /tmp
sudo apt-get build-dep pygame
apt-get source pygame
vim pygame-1.9.1release+dfsg/src/joystick.c
# search for the printf("SDL.. messages and put a // in front
apt-get source --compile pygame
sudo dpkg -i python-pygame_1.9.1release+dfsg-9ubuntu1_amd64.deb

Greetings Max

Answer 2

Building on @charleslparker's answer:

from contextlib import contextmanager
import sys, os

@contextmanager
def suppress_stdout():
    with open(os.devnull, "w") as devnull:
        old_stdout = sys.stdout
        sys.stdout = devnull
        try:  
            yield
        finally:
            sys.stdout = old_stdout

print("Now you see it")
with suppress_stdout():
    print("Now you don't")

Tests

>>> with suppress_stdout():
        os.system('play /mnt/Vancouver/programming/scripts/PHASER.WAV')

/mnt/Vancouver/programming/scripts/PHASER.WAV:

 File Size: 1.84k     Bit Rate: 90.4k
  Encoding: Unsigned PCM  
  Channels: 1 @ 8-bit    
Samplerate: 11025Hz      
Replaygain: off         
  Duration: 00:00:00.16  

In:100%  00:00:00.16 [00:00:00.00] Out:1.79k [!=====|=====!]        Clip:0    
Done.

Use this to completely suppress os.system() output:

>>> with suppress_stdout():
        os.system('play /mnt/Vancouver/programming/scripts/PHASER.WAV >/dev/null 2>&1')
>>> ## successfully executed

>>> import time
>>> with suppress_stdout():
        for i in range(3):
                os.system('play /mnt/Vancouver/programming/scripts/PHASER.WAV >/dev/null 2>&1')
                time.sleep(0.5) 
>>> ## successfully executed

Useful (e.g.) to signal completion of long-running scripts.

Answer 3

Here's the relevant block of code from joystick.c (via SVN at http://svn.seul.org/viewcvs/viewvc.cgi/trunk/src/joystick.c?view=markup&revision=2652&root=PyGame)

    value = SDL_JoystickGetHat (joy, _index);
#ifdef DEBUG
    printf("SDL_JoystickGetHat value:%d:\n", value);
#endif
    if (value & SDL_HAT_UP) {

Looks like a problem with having debugging turned on.

Answer 4

Just for completeness, here's a nice solution from Dave Smith's blog:

from contextlib import contextmanager
import sys, os

@contextmanager
def suppress_stdout():
    with open(os.devnull, "w") as devnull:
        old_stdout = sys.stdout
        sys.stdout = devnull
        try:  
            yield
        finally:
            sys.stdout = old_stdout

With this, you can use context management wherever you want to suppress output:

print("Now you see it")
with suppress_stdout():
    print("Now you don't")

Answer 5

I use pythonw.exe (on Windows) instead of python.exe. In other OSes, you could also redirect output to /dev/nul. And in order to still see my debug output, I am using the logging module.

Answer 6

To complete charles's answer, there are two context managers built in to python, redirect_stdout and redirect_stderr which you can use to redirect and or suppress a commands output to a file or StringIO variable.

import contextlib

with contextlib.redirect_stdout(None):
    do_thing()

For a more complete explanation read the docs

A quick update: In some cases passing None might raise some reference errors (e.g. keras.models.Model.fit calls sys.stdout.write which will be problematic), in that case pass an io.StringIO() or os.devnull.