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Binary data exchange

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I have a pair of simple python programs as follows:

#!/usr/bin/python
# broadcast.py
import socket
from ctypes import *
import random

class PurgeData(Structure):
    _fields_ = [("press",c_int), ("ticks",c_int), ("volume",c_float)]
    
myPort = 10756

sock=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
addr = ('localhost',myPort)
#sock.sendto(data,addr)

presdata = PurgeData()
presdata.press = 0
presdata.ticks = 100
    
for msg in range(1,20):
    presdata.press = presdata.press+1
    presdata.ticks = presdata.ticks+1
    presdata.volume = random.random()
    sock.sendto(presdata,addr)

#--------------------

#!/usr/bin/python
# Receiver
import socket

from ctypes import *

class PurgeData(Structure):
    _fields_ = [("press",c_int), ("ticks",c_int), ("volume",c_float)]
    
myPort = 10756

sock=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
addr = ('localhost',myPort)
sock.bind(addr)
presdata=PurgeData()
    
while True:
    data,addr = sock.recvfrom(1024)
    memmove(addressof(presdata),data.strip(),len(data.strip()))
    print presdata.press, presdata.ticks, presdata.volume

---------------------

When I tried to run this I get some bizarre results:


1 101 0.343009024858
2 102 0.36397305131
3 103 0.495895296335
4 104 0.372055351734
5 105 0.933839201927
6 106 0.931187808514
7 107 0.876732826233
8 108 0.298638045788
1828716544 -754974720 0.183644190431
1845493760 1660944384 0.186560109258
1862270976 1056964608 0.18631502986
1879048192 1728053248 0.186902835965
1895825408 2097152000 0.18658298254
14 114 0.407857120037
15 115 0.833854913712
16 116 0.00646247947589
17 117 0.297783941031
18 118 0.58082228899
19 119 0.61717569828

the received data for the messages 9 thru 13 are not as expected.

I wonder if anyone can see what I am doing wrong?

Appreciate any hints. thanks, srini

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Binary data exchange "RasikaSrinivasan@gmail.com" <RasikaSrinivasan@gmail.com> - 2014-05-29 15:08 -0700
  Re: Binary data exchange "RasikaSrinivasan@gmail.com" <RasikaSrinivasan@gmail.com> - 2014-05-29 15:13 -0700
  Re: Binary data exchange MRAB <python@mrabarnett.plus.com> - 2014-05-30 00:09 +0100
    Re: Binary data exchange "RasikaSrinivasan@gmail.com" <RasikaSrinivasan@gmail.com> - 2014-05-29 16:25 -0700
      Re: Binary data exchange Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-30 00:56 +0100
  Re: Binary data exchange Ian Kelly <ian.g.kelly@gmail.com> - 2014-05-29 17:20 -0600

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