# works on Mac OS X and Linux. haven't tried BSD. obviously windows is out.

import os
import subprocess
import signal

def get_tty_fg():
    # make a new process group within the same session as the parent. we
    # do this so that if the user hits ctrl-c, etc in the curses program
    # that's about to be exec'd, the SIGINT and friends won't be sent to
    # the parent.
    os.setpgrp()

    # don't stop the process when we get SIGTTOU. since this is now in a
    # background process group, SIGTTOU will be sent to this process when
    # we call tcsetpgrp(), below. the default action when receiving that
    # signal is to stop (process mode T).
    hdlr = signal.signal(signal.SIGTTOU, signal.SIG_IGN)

    # open a file handle to the current tty
    tty = os.open('/dev/tty', os.O_RDWR)

    # ask for our new process group to be the foreground one on the
    # controlling tty.
    os.tcsetpgrp(tty, os.getpgrp())

    # replace the old signal handler to minimize the chance of the child
    # getting confused by a non-standard starting signal table.
    signal.signal(signal.SIGTTOU, hdlr)

def spawn_pager(path):
    # should always allow users to configure their own pager. "pager" by
    # itself is a better default than less on Debian-based systems, but
    # that's not everywhere. Best default to "less" for maximum
    # compatibility.
    pager = os.environ.get('PAGER', 'less')

    # if your calling process also expects to use the tty, you'll need to
    # do some extra stuff here to stop using it and handle SIGTTOU, SIGHUP,
    # and possibly SIGTTIN, as appropriate, until the child is done.

    # run with our tty-foreground code in the child before exec'ing the
    # pager. return the pager process object.
    return subprocess.Popen([pager, path], preexec_fn=get_tty_fg)