human
Complete this python program:
def i3_subscribe(conn, event, callback):
assistant
#Here is the Python code you requested.

    """Subscribe to i3 workspace event
    :param conn:
    Connection returned by :py:func:`get_i3_connection`.
    :param str event:
    Event to subscribe to, e.g. ``\workspace\``.
    :param func callback:
    Function to run on event.
    """
    try:
        import i3
    except ImportError:
        pass
    else:
        conn.Subscription(callback, event)
        return
    conn.on(event, callback)
    from threading import Thread
    class I3Thread(Thread, ):
        daemon = True
        def __init__(self, conn):
            super(I3Thread, self).__init__()
            self.__conn = conn
        def run(self):
            self.__conn.main()
    thread = I3Thread(conn=conn)
    thread.start()