This is the default shutdown callback that is set on the options.
    It prints out a message to stderr that informs the user that some events
    are still pending and the process is waiting for them to flush out.

def default_callback(pending, timeout):
    """This is the default shutdown callback that is set on the options.
    It prints out a message to stderr that informs the user that some events
    are still pending and the process is waiting for them to flush out.
    """

    def echo(msg):
        sys.stderr.write(msg + "\n")

    echo("Sentry is attempting to send %i pending error messages" % pending)
    echo("Waiting up to %s seconds" % timeout)
    echo("Press Ctrl-%s to quit" % (os.name == "nt" and "Break" or "C"))
    sys.stderr.flush()