Python - Sending hex array via UDP

Question

Yes I know UDP is bad but unfortunately I have no choice - my server only takes UDP...

What I have is a list that contains hex values, need to send that out UDP.

If I try and send the list I get - 'TypeError: must be string or buffer, not list'

If i convert to a string (called aList in my code) I get - 'TypeError: an integer is required' Print of aList = 09004000e3f00005f5

if I convert aList to an int with base 16 I get - 'TypeError: must be string or buffer, not long'

Suspect it's something basic but I'm missing it.

Simple code looks like::

import socket   #for sockets    

UDP_PORT    = 21105;
UDP_HOST    = '10.194.34.151';


z21 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

def _getLocoInfo (id):
    arr        = [ 0x09, 0x00, 0x40, 0x00, 0xE3, 0xF0, 0x00, id]
    arr.append(arr[5]^arr[6]^arr[7])
    return arr

msg = _getLocoInfo(0x05)
aList = "".join("%02x" % b for b in msg)

print (a)

try :
    z21.send(msg ,(UDP_HOST, UDP_PORT) )
     # receive data from client (data, addr)
    d = s.recvfrom(1024)

    print ('Server reply : ' + reply)

except socket.error as e:
        print ('Error Code : ' + str(e[0]) + ' Message ' + e[1])
        sys.exit()

Are you using Python 2 or 3?

jython234
– jython234

2016-04-12 00:15:33 +00:00
Commented Apr 12, 2016 at 0:15 — jython234
– jython234, Commented Apr 12, 2016 at 0:15

rufism · Accepted Answer · 2016-04-11 22:29:24Z

1

I'm not very knowledgeable when it comes to python's socket module but looking at this page I feel you are missing two things:

try using z21.sendto instead of z21.send
try converting your message to a byte buffer with bytes()

So the result would look like this:

... other code

try:
  z21.sendto(bytes(msg) ,(UDP_HOST, UDP_PORT))

... following code

I hope this helps.

answered Apr 11, 2016 at 22:29

rufism

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1 Comment

MikeM Over a year ago

Well would you look at that. Don't I feel like a dumbass. That looks like it sends now but no response back so time to fire up wireshark. But at this stage looks good.

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