non-blocking sockets and generators

[Gary Stephenson]

I'm playing around with combining non-blocking sockets with generators -
which is probably really stupid 'coz I don't know terribly much about either
but, hey ..  I _am_ learning....

Anyway, I suspect my first question has nothing to do with non-blocking
sockets _or_ generators, albeit that both appear in the code.  Why does this
:

    def socketAccept( self, s ) :
        while True :
            try :
                ( sock, addr ) = s.accept()
            except :
                yield None
            self.addThread( self.createThread( sock, addr ) )

yield the following error ? (running under Pythonwin) :

    self.addThread( self.createThread( sock, addr ) )
UnboundLocalError: local variable 'sock' referenced before assignment

Also, I'd like to be a touch more specific ;-) in the except clause, but I
can't seem to figure out the appropriate exception class to use.  The socket
docs talk about non-blocking sockets raising
"a 'error' exception", but when I tried to use "except error : "  I got

NameError: global name 'error' is not defined

What exception class (if any) should be used to catch the non-blocking
socket's exception?

many tias,

gary