<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _systemd_notify_once():
 """Send notification once to Systemd that service is ready. Systemd sets NOTIFY_SOCKET environment variable with the name of the socket listening for notifications from services. This method removes the NOTIFY_SOCKET environment variable to ensure notification is sent only once. """


        notify_socket = os.getenv('NOTIFY_SOCKET')
        if notify_socket:
            if notify_socket.startswith('@'):
                # abstract namespace socket
                notify_socket = '\0%s' % notify_socket[1:]
            sock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
            with contextlib.closing(sock):
                try:
                    sock.connect(notify_socket)
                    sock.sendall(b'READY=1')
                    del os.environ['NOTIFY_SOCKET']
                except EnvironmentError:
                    LOG.debug("Systemd notification failed", exc_info=True)