On Mon, 13 Oct 2008 16:49:03 +0200, Peter Jacobi <pjacobi.de@googlemail.com> wrote:

Dear All,

I've just started diving into Twisted, read the docs, run the samples, wrote some tests, but:

I'm rather clueless about some architectural decisions in Twisted Core, and perhaps somebody can clarify whether these are just hictorical accidents or serve a purpose I didn't get yet.

Specifically I don't understand why the Factory classes in internet/protocols.py rely on class variables instead of instance variables for, most importantly "protocol", but also for "noisy" and "numPorts"?

Won't this introduce an unwanted coupling between different instances of Factory, and effectively make the creation of more than instance of any Factory-derived class pointless (or even incorrect). Sort of a singleton pattern relying on the trust principle?

Factories don't "rely" on class *attributes*. Attribute lookup on instances in Python first checks the instance dictionary then the class dictionary. If an attribute is found on the instance, then the class is ignored. So when you are setting attributes such as `noisy´ or `protocol´, if you want the change to only modify the behavior of one instance, then set the attribute on an instance, not on the class. Jean-Paul