[1.7.x] Fixed #20815 -- Don't enforce unbuffered I/O on Python 3.

import os

import sys

from . import six

buffering = int(six.PY3)        # No unbuffered text I/O on Python 3 (#20815).

if os.name == 'posix':

    def become_daemon(our_home_dir='.', out_log='/dev/null',

                      err_log='/dev/null', umask=0o022):

            os._exit(1)

        si = open('/dev/null', 'r')

        so = open(out_log, 'a+', 0)

        se = open(err_log, 'a+', 0)

        so = open(out_log, 'a+', buffering)

        se = open(err_log, 'a+', buffering)

        os.dup2(si.fileno(), sys.stdin.fileno())

        os.dup2(so.fileno(), sys.stdout.fileno())

        os.dup2(se.fileno(), sys.stderr.fileno())

        sys.stdout.close()

        sys.stderr.close()

        if err_log:

            sys.stderr = open(err_log, 'a', 0)

            sys.stderr = open(err_log, 'a', buffering)

        else:

            sys.stderr = NullDevice()

        if out_log:

            sys.stdout = open(out_log, 'a', 0)

            sys.stdout = open(out_log, 'a', buffering)

        else:

            sys.stdout = NullDevice()