> The value is used there, but this is not effective in causing larger
> packets to be sent, which I noticed by watching with strace.  I think
> the reason for this is that 'refill_buffer' will only make at most one
> call to simple_producer.more, and that call will produce at most 512
> bytes, because that's the default value of that argument, and its not
> overridden in the call that creates the simple_producer inside of 
> 'push'.

Sorry, you're right. 
I remember now that I reported a similar thing in bug #1736190:
http://bugs.python.org/msg57581

> In addition, I see at least one other place in the code where the
> constant '512' appears.

Where? Aside from simple_producer.__init__ I don't see other places
where it is used.