multi-Singleton-like using __new__

[J Peyret]

On Feb 8, 5:38 pm, Freek Dijkstra <fr... at macfreek.nl> wrote:

If you want to subclass, my initial example did not cover that.  This
will, or at least, I don't have any problems with similar code:

 ...     def __new__(cls,uri,*args,**kwds):
...         try:
...             return cls.cache[(cls,uri)]  #notice that I added the
class itself as a key.
...         except KeyError:
...             print "cache miss"
...             res = cls.cache[(cls,uri)] = object.__new__(cls)
...             return res

Your mileage apparently varies, but I'm still not sold on using a
metaclass.  Just because it is a bit fancy for the requirements,
IMHO.  Later you may have cached/singleton classes that really need a
metaclass for something else, with subclasses of _those_ that don't
want caching.  That's definitely just my $.02 there, I don't
necessarily expect others to share my prejudices and misgivings.

Anyway, I should post answers more often - I learned more today than
by asking questions ;-)  Txs all, for the has_key/in performance
pointers, they are exactly contrary to what I would have thought.

Cheers