UDP socket, need help setting sending port

[Steve Horsley]

Sells, Fred wrote:
> I'm using MSW XP Pro with Python 2.4 to develop but production will be Linux
> with Python 2.3.  (could upgrade to 2.4 if absolutely necessary) I can also
> switch to Linux for development if necessary.
> 
> I am writing some python to replace proprietary software that talks to a
> timeclock via UDP.
> 
> The timeclock extracts the sending port from the UDP header and uses that
> for all response messages.
> 
> I cannot find out how to set the sending port in the header.  Windows XP
> appears to set an arbitrary port.  I've been using ethereal to analyze
> network traffic and it seems that if I can set the sending port, I should be
> OK.
> 
> I have been googling various combinations of "python udp ..." for the last
> two hours and have not found anything that addresses how to set the sending
> port.  I'm guessing that this may be in setsockopt but don't see any
> parameters that "click".


Try binding the address ('',0) which means any address, any port 
on this box. Then get the bound address with getsockname(). Below 
is a copy of an interactive try-out...



 >>> import socket
 >>> s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
 >>> s.bind(('',0))
 >>> s
<socket._socketobject object at 0xb7d9ee0c>
 >>> s.getsockname()
('0.0.0.0', 32775)
 >>>

So in this case, port 32775 was chosen to bind to.

Steve