How to tell when a socket is closed on the other end?

Roy Smith roy at
Wed Jul 25 16:37:00 CEST 2007

In article <1185371863.622473.205010 at>,
 billiejoex <gnewsg at> wrote:

> Hi there.
> I'm setting up test suite for a project of mine.
> >From test suite, acting as a client, I'd like to know, in certain
> situations, if the socket is closed on the other end or not.
> I noticed that I can "detect" such state if a call to
> returns 0 but it seems a little poor to me. :-\
> Is there a reliable way to test such socket 'state'?

This isn't really a Python question, it's a Berkeley Socket API question.  
You don't say, but I assume you're talking about a TCP (i.e. SOCKSTREAM) 

The answer is you can use the select() system call to detect "exceptional 
conditions" on a socket.  Python's select module provides this 
functionality, but to understand how to use it, you need to study the 
underlying API.

On the other hand, returning 0 works too.  What do you find 
"poor" about that?  What do you want to know about the connection being 
closed that you don't find out by getting 0 back from read()?

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