Question

Is it possible to send an array through UDP Sockets using Python? I am using Python 2.5 and trying to send a simple array but it’s not working. It can send the array successfully but when I try to print it with an item of the array the program crashes. I’m not sure what the error is as I take the precaution of converting the data into an array but it’s not working. Hope I explained the problem as clearly as possible. I would appreciate the help!

# Client program

from socket import *
import numpy
from array import*

# Set the socket parameters
host = "localhost"
port = 21567
buf = 4096
addr = (host,port)

# Create socket
UDPSock = socket(AF_INET,SOCK_DGRAM)

def_msg = "===Enter message to send to server===";
print "\n",def_msg
a = array('i',[1,3,2])
# Send messages
while (1):
    data = raw_input('yes or now')
    if data!= "yes":
        break
    else:
        if(UDPSock.sendto(a,addr)):
            print "Sending message"

# Close socket
UDPSock.close()



# Server program

from socket import *

# Set the socket parameters
host = "localhost"
port = 21567
buf = 4096
addr = (host,port)

# Create socket and bind to address
UDPSock = socket(AF_INET,SOCK_DGRAM)
UDPSock.bind(addr)

# Receive messages
while 1:
    data,addr = UDPSock.recvfrom(buf)
    L = eval(data)
    if not data:
        print "Client has exited!"
        break
    else:
        print "\nReceived message '", L[1],"'"

# Close socket
UDPSock.close()

Answer 1

eval is doing something completely different than what you think.

To send data over network, you need to serialize it into an array of bytes, then deserialize it back. In Python, serialization of most objects can be done via pickle module:

if (UDPSock.sendto( pickle.dumps(a), addr)):

Deserialization:

data,addr = UDPSock.recvfrom(buf)
L = pickle.loads(data)
print repr(L) # prints array('i', [1, 3, 2])