Event Driven programming - Doubts

[Jean-Paul Calderone]

On Mon, 22 Dec 2008 06:57:55 -0800 (PST), Kottiyath <n.kottiyath at gmail.com> wrote:
>Hi,
>    I have been looking at Twisted and lately Circuits as examples for
>event driven programming in Python.
> [snip]
>
>    My question is as follows:
>    I have not understood how the callbacks are hit without (a)
>blocking the code or (b) having new threads.

There is blocking code - but just in one place.  For example,

http://twistedmatrix.com/trac/browser/trunk/twisted/internet/selectreactor.py#L93

Jean-Paul