[zeromq-dev] Change of type after sending over

[Jon Dyte]

On 26/12/11 06:27, Hor Meng Yoong wrote:
> Hi:
>
> import struct
> import time
> import zmq
> from zmq.eventloop import ioloop, zmqstream
> loop = ioloop.IOLoop.instance()
>
> ctx = zmq.Context()
> s = ctx.socket(zmq.REP)
> s.bind('tcp://127.0.0.1:5555 <http://127.0.0.1:5555>')
> stream = zmqstream.ZMQStream(s, loop)
>
> def echo(msg):
>   print('receive', msg, len(msg))
>   print('Type of ', msg, 'is ', type(msg))
>   (a,), msg = struct.unpack('B', msg[:1]), msg[1:]
>   print('a = %c ' % a)
>   if (a == 'A'):
>     stream.send(b'a')
>   elif (a == 'B'):
>     stream.send(b'b')
>   else:
>     stream.send(b'z')
>
> stream.on_recv(echo)
> loop.start()
>
> *Type of  [b'ABCD'] is <class 'list'>*
>
> As the received msg is in list, I could not use struct.unpack:
> TypeError: 'list' does not support the buffer interface
>
> Is this a bug or a normal behavior for zmq send()/receive() to change 
> the type?
>
> Regards
> Hor Meng

Hi

The type is not being changed.
The ZMQStream method on_recv calls the the callback ('echo') passing a 
python list of all the messages received.
This is so that if a multipart message is sent the callback gets called 
with all the message parts.

In the echo callback , you need to iterate over the list of messages passed.
It's described here:-
http://zeromq.github.com/pyzmq/api/generated/zmq.eventloop.zmqstream.html

Jon





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