Suppressing output of module calling outside library

Question

I have an annoying problem when using machine learning library PyML. PyML uses libsvm to train the SVM classifier. The problem is that libsvm outputs some text to standard o

Answer 1

Dave Smith gave a wonderful answer to that on his blog. Basically, it wraps Ignacio's answer nicely:

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

Now, you can surround any function that garbles unwanted noise into stdout like this:

print "You can see this"
with suppress_stdout():
    print "You cannot see this"
print "And you can see this again"

For Python 3 you can use:

from contextlib import contextmanager
import os
import sys

@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

Answer 2

I had the same problem and fixed it like that:

from cStringIO import StringIO

def wrapped_svm_predict(*args):
    """Run :func:`svm_predict` with no *stdout* output."""
    so, sys.stdout = sys.stdout, StringIO()
    ret = svm_predict(*args)
    sys.stdout = so
    return ret

Answer 3

I had a similar problem with portaudio/PyAudio initialization. I started with Reid's answer, which worked. Although I needed to redirect stderr instead. So, here is an updated, cross-platform version that redirects both:

import sys, os

# hide diagnostic output
with open(os.devnull, 'w') as devnull:
    # suppress stdout
    orig_stdout_fno = os.dup(sys.stdout.fileno())
    os.dup2(devnull.fileno(), 1)
    # suppress stderr
    orig_stderr_fno = os.dup(sys.stderr.fileno())
    os.dup2(devnull.fileno(), 2)

    print('*** stdout should be hidden!  ****')
    print('*** stderr should be too!  ****',
          file=sys.stderr)

    os.dup2(orig_stdout_fno, 1)  # restore stdout
    os.dup2(orig_stderr_fno, 2)  # restore stderr

print('done.')

Should be easy to comment out a part you don't need.

Answer 4

Open /dev/null for writing, use os.dup() to copy stdout, and use os.dup2() to copy your open /dev/null to stdout. Use os.dup2() to copy your copied stdout back to the real stdout after.

devnull = open('/dev/null', 'w')
oldstdout_fno = os.dup(sys.stdout.fileno())
os.dup2(devnull.fileno(), 1)
makesomenoise()
os.dup2(oldstdout_fno, 1)