How to suppress console output in Python?

问题:

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 I use the console to help me debug and now it gets flooded with SDL_JoystickGetHat value:0: 60 times every second. Is there a way I can disable this? Either through an option in Pygame/SDL or suppress console output while the function calls? I saw no mention of this in the Pygame documentation.

edit: This turns out to be due to debugging being turned on when the SDL library was compiled.

回答1:

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.

回答2:

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")

回答3:

You can get around this by assigning the standard out/error (I don't know which one it's going to) to the null device. In Python, the standard out/error files are sys.stdout/sys.stderr, and the null device is os.devnull, so you do

sys.stdout = os.devnull
sys.stderr = os.devnull

This should disable these error messages completely. Unfortunately, this will also disable all console output. To get around this, disable output right before calling the get_hat() the method, and then restore it by doing

sys.stdout = sys.__stdout__
sys.stderr = sys.__stderr__

which restores standard out and error to their original value.

回答4:

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

回答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.

回答6:

As Demolishun mentions in an answer to a closed duplicate question, there is a thread talking about this issue. The thread is from August of 2009 and one of the developers says the debug code was left in on accident. I had installed Pygame 1.9.1 from pip and the debug output is still present.

To get around it for now, I downloaded the source from pygame.org, removed the print statements from src/joystick.c and compiled the code.

I am on OS X 10.7.5 for what it's worth.

回答7:

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