On Sat, 30 Jun 2012 02:28:52 +0000, Steven D'Aprano wrote: > On Fri, 29 Jun 2012 19:41:11 +0000, Alister wrote: > >> also this section in main strikes me as a bit odd and convoluted >> >> w = world() >> serv = server(client) >> w.server = serv serv.world = w >> >> I think you are cross referencing classes & would be better to >> investigate inheritance. > > What you show above is composition, and is a perfectly valid technique, > and in fact should often be *preferred* to inheritance. > > The only slightly dubious part, and I stress *slightly*, is that there > is a circular reference: w refers to serv, and serv refers back to w. > While legitimate, it is a very slight "code smell" that should be > investigated. > If there is a way to get the same result without the circular reference, > that would be preferred. > > For example, perhaps server methods that need to know the world could > take it as an explicit argument, rather than fetching it implicitly from > server.world. > > Or, a moderately advanced technique, use a weak-ref instead. > > Inheritance should only be used to model "is-a" relationships. For > example, Herbie the Love Bug is a Volkswagen Beetle, so inheritance is > appropriate. > > http://en.wikipedia.org/wiki/Herbie > > > class Vehicle(object): > pass > > class Car(Vehicle): > pass > > class Beetle(Car): > pass > > herbie = Beetle() > > Composition should be used to model "has-a" relationships. For example, > a car has an engine, it is not a kind of engine, and so inheritance is > inappropriate and composition should be used. I would re-write the Car > class as follows: > > class Engine(object): > pass > > class Car(Vehicle): > def __init__(self): > self.engine = Engine() > > So now we can talk about Herbie's engine: > > herbie.engine # Herbie, being a car, has an engine, he is not an engine
I probably was not to clear (due to my own inexperience) it was the circular references that grabbed my attention, it may be OK but suggests to me there may be a better approach. -- ((lambda (foo) (bar foo)) (baz)) -- http://mail.python.org/mailman/listinfo/python-list
