Strange UDPServer behaviour

Peter Hansen peter at engcorp.com
Mon Mar 31 16:01:14 CEST 2003


Ulf von Ceumern wrote:
> 
> However, whenever i send a udp datagram to the server and print the
> request, i get 5 times the same message.
> 
> -----------------
> the test-client:
> -----------------
> 
> import socket
> 
> spamHosts=("127.0.0.1")

Did you intend to make this a tuple?  It's not a tuple right now...
To make a one-element tuple, you must add a trailing comma, to
let the compiler know you didn't mean for this just to be an 
expression in parentheses:

spamHosts = ("127.0.0.1", ) # trailing comma required here

A "better" solution is to always use lists when you are expecting
to have a list of things, even if you don't plan to change the 
contents of the list.  Use tuples to represent "static collections
of different data types", as with C structs.  (In spite of Guido's
reported recent suggestions to the contrary, where he apparently
didn't encourage this view of lists and tuples.)

spamHosts = ["127.0.0.1"] # trailing comma is optional in lists

> spamPort=5456
> 
> class spamlog:
>     def __init__(self):
>  self.spamSocket=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
> 
>     def send(self,f,ip):
>  for ipdest in spamHosts:
>      self.spamSocket.sendto("%s|%s"%(f,ip),(ipdest,spamPort))

Above, you are probably iterating one character at a time through your
string, rather than once through a tuple.

> ----------------
> the output when i call udpsend.py once:
> ----------------
> bash-2.03$ ./testd.py
> heinbloed at kutter.de|192.192.192.192
> heinbloed at kutter.de|192.192.192.192
> heinbloed at kutter.de|192.192.192.192
> heinbloed at kutter.de|192.192.192.192
> heinbloed at kutter.de|192.192.192.192
> -----------------
> why 5 times??? this is driving me crazy.

Probably it would have gone for len("127.0.0.1") times, except for
something like the backlog in TCP (is there anything similar in UDP?)
but I doubt it's directly relevant to the problem.

I *suspect* this is what went wrong, but I haven't tried your 
code to test the theory nor, I'm afraid, really analyzed the
rest of your code to see if this is likely.

-Peter




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