Cristiano Paris wrote: > I'm trying to write a Container which should mimic a list. Basically, > the container pulls items on the fly from an unspecified source through > a function and returns an instance of a given class over the pulled item. > > That is: > > class lazy(object): > def __getitem__(self,index): > return Foo(f(index)) > > lc = lazy() > > Here I see a problem: two consecutive accesses to lc for the same index > would retrieve two different instances of Foo. > > In some scenarios this is not desirable since one wants to have all the > accessors to share the same instance for the same index so as to reduce > memory consumption. > > So, I thought to use an internal dictionary of all the Foo instances > given away so far. Something like:
> The problem with this implementation is that the cache never decreases > in length as Foo instances are no longer referenced by the lc accessor > since they're all referenced by the internal cache. You want a WeakValueDictionary: http://docs.python.org/lib/module-weakref.html Peter -- http://mail.python.org/mailman/listinfo/python-list
