[Tutor] Don't understand this class/constructor call syntax

[dave]

I was dimly aware of the functioning of booleans, but I see now that it
doesn't specify an actual boolean type.  Still, the code confuses me.  Is the
usage of pad_for_usrp consistent with it being treated as a boolean?  Why
would the entire self reference be transmitted then?

Example code again:

class transmit_path(gr.top_block)
[...]
    self.packet_transmitter = ieee802_15_4_pkt.ieee802_15_4_mod_pkts(self,
spb=self._spb, msgq_limit=2)

The class from the ieee802_15_4_pkt module:

class ieee802_15_4_mod_pkts(gr.hier_block2):
    """
    IEEE 802.15.4 modulator that is a GNU Radio source.

    Send packets by calling send_pkt
    """
    def __init__(self, pad_for_usrp=True, *args, **kwargs): 
        """
	Hierarchical block for the 802_15_4 O-QPSK  modulation.

        Packets to be sent are enqueued by calling send_pkt.
        The output is the complex modulated signal at baseband.

        @param msgq_limit: maximum number of messages in message queue
        @type msgq_limit: int
        @param pad_for_usrp: If true, packets are padded such that they end up
a multiple of 128 samples

        See 802_15_4_mod for remaining parameters
        """
	try:
		self.msgq_limit = kwargs.pop('msgq_limit') 
	except KeyError:
		pass

	gr.hier_block2.__init__(self, "ieee802_15_4_mod_pkts",
		gr.io_signature(0, 0, 0),                     # Input
		gr.io_signature(1, 1, gr.sizeof_gr_complex))  # Output
        self.pad_for_usrp = pad_for_usrp

        # accepts messages from the outside world
        self.pkt_input = gr.message_source(gr.sizeof_char, self.msgq_limit)
        self.ieee802_15_4_mod = ieee802_15_4.ieee802_15_4_mod(self, *args,
**kwargs)
        self.connect(self.pkt_input, self.ieee802_15_4_mod, self)

    def send_pkt(self, seqNr, addressInfo, payload='', eof=False):
        """
        Send the payload.

        @param seqNr: sequence number of packet
        @type seqNr: byte
        @param addressInfo: address information for packet
        @type addressInfo: string
        @param payload: data to send
        @type payload: string
        """

        if eof:
            msg = gr.message(1) # tell self.pkt_input we're not sending any
more packets
        else:
            FCF = make_FCF()

            pkt = make_ieee802_15_4_packet(FCF,
                                           seqNr,
                                           addressInfo,
                                           payload,
                                           self.pad_for_usrp)
             #print "pkt =", packet_utils.string_to_hex_list(pkt), len(pkt)
            msg = gr.message_from_string(pkt)

        #ERROR OCCURS HERE (a few functions in while inserting onto the msg queue)
        self.pkt_input.msgq().insert_tail(msg)
------- End of Forwarded Message -------