buggy output capturing

MutedOutput.py

class MutedOutput(object):
    def __init__(self):
        self.null_fds = [os.open(os.devnull, os.O_RDWR) for _ in xrange(2)]
        self.savd_fds = None
        self.pipe = os.pipe() # (r, w) FDs tuple

    def __enter__(self):
        self.savd_fds = os.dup(1), os.dup(2)
        #os.dup2(self.null_fds[0], 1)
        os.dup2(self.pipe[1]    , 1)
        os.dup2(self.null_fds[1], 2)

        # XXX: I'd like to return os.fdopen(self.pipe[0]) but it blocks
        return self.pipe[0]

    def __exit__(self, type, value, traceback):
        os.dup2(self.savd_fds[0], 1)
        os.dup2(self.savd_fds[1], 2)

        os.close(self.pipe[0])
        os.close(self.pipe[1])

        os.close(self.savd_fds[0])
        os.close(self.savd_fds[1])

        os.close(self.null_fds[0])
        os.close(self.null_fds[1])