Sending data over TCP from arduino to python

Question

I've been struggling with this for a few hours now and really just don't know where to go from here. I've got an arduino uno with a wifi shield connected to a network, and a laptop with Ubuntu connected to the same network. I'm using the arduino Wifi Library to connect to the network.

I can send data to my laptop from the arduino and print it successfully using: sudo nc -l 25565

I am also trying to use the following python code to do the same thing I did with nc which is also being run as sudo just in case:

#!/usr/bin/env python

import socket

TCP_IP = '127.0.0.1'
TCP_PORT = 25565
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP,TCP_PORT))
s.listen(1)

(conn,addr) = s.accept()
print 'Connection address: ',addr
while True:
    data = conn.recv(BUFFER_SIZE)
    if not data: break
    print 'received data: ',data
    conn.send('ECHO')
conn.close()
s.close()

But it just hangs at (conn,addr) = s.accept(). Using a client python script on the same laptop I can connect to the above server and I can send data to it which the server then prints.

I just have no idea why nc will print from the arduino but the python server script won't, even though it will print from a python client. Could the arduino libraries be failing to follow some standard that python expects? Thanks in advance.

Robᵩ · Accepted Answer · 2014-10-09 12:52:56Z

No, the arduino libraries are not "failing to follow some standard".

Your program is binding to the localhost interface, IP address 127.0.0.1. This means that only programs running on the same PC will be able to connect to your Python server.

Try this:

s.bind(('',TCP_PORT))

Reference:

https://docs.python.org/2/library/socket.html :

For IPv4 addresses, two special forms are accepted instead of a host address: the empty string represents INADDR_ANY, and the string '<broadcast>' represents INADDR_BROADCAST. The behavior is not available for IPv6 for backward compatibility, therefore, you may want to avoid these if you intend to support IPv6 with your Python programs.

https://docs.python.org/2/howto/sockets.html#creating-a-socket :

A couple things to notice: we used socket.gethostname() so that the socket would be visible to the outside world. If we had used s.bind(('localhost', 80)) or s.bind(('127.0.0.1', 80)) we would still have a “server” socket, but one that was only visible within the same machine. s.bind(('', 80)) specifies that the socket is reachable by any address the machine happens to have.

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