A simple context manager to redirect output written to given file object to another one or to discard the data entirely.

fileredir.py

import os

class _FileRedirect(object):
    """
    A simple context manager to redirect output written to given file object
    to another one or to discard the data entirely.
    
    It works at OS level to allow to redirect/discard output from libraries
    written in C too. This means that only file-like objects working on real
    file descriptors are supported (sys.stdout, sys.stderr or any file opened
    using the ``open`` or ``os.fdopen`` functions).
    """

    def __init__(self, f, to=None):
        """
        Omitting the ``to`` argument causes the output to be discarded
        """
        self.f = f
        self.to = to
        self.fd = f.fileno()

    def __enter__(self):
        self.f.flush()
        self.old = os.dup(self.fd)
        
        if self.to is None:
            os.close(self.fd)
            os.open(os.devnull, os.O_CREAT|os.O_WRONLY) == self.fd
        else:
            os.dup2(self.to.fileno(), self.fd)

    def __exit__(self, type, value, traceback):
        self.f.flush()
        
        if self.to is not None:
            self.to.flush()
        
        os.dup2(self.old, self.fd)
        os.close(self.old)

def discard(fh):
    """
    Functional wrapper around the ``_FileRedirect`` context manager to discard
    data printed to the given file object.
    """
    return _FileRedirect(fh, None)


def redirect(from_fh, to_fh):
    """
    Functional wrapper around the ``_FileRedirect`` context manager to redirect
    data written to a file to another one.
    """
    return _FileRedirect(from_fh, to_fh)


# Use it like this:

import sys

def verbose():
    print "Hello world\n" * 100

with discard(sys.stdout):
    verbose()

# or:

def not_an_error():
    print >>sys.stderr, "Hello world"

with redirect(sys.stderr, sys.stdout):
    not_an_error()