On Tue, Jun 19, 2012 at 10:15:03PM +0200, Vincent Pelletier wrote: > Le mardi 19 juin 2012 19:54:21, Claudiu Saftoiu a écrit : > > def calc_it(self, b): > > if not hasattr(self, 'b_cache'): self.b_cache = > > PersistentDict() > > If you were to use this, you would probably prefer to do > try: > self.b_cache > except AttributeError: > self.b_cache = PersistentDict() > (assigning the result to a vairable, etc) > as this is faster when b_cache is actually here (which is much more likely > than not). Also, it avoids hiding too many exceptions, as with hasattr. In > the > times of ReadConflictError it was quite important (at least to stop > processing > earlier on a doomed transaction). I'm not sure how important this is nowadays > - I just kept the habit of avoiding "hasattr" on persistent objects. > > > The former is OK, but if I have multiple functions that want to use the new > > functionality I'll have to have the code all over, and it won't be obviously > > separated. > > Maybe a @property taking care of creating the actual PersistentDict if not > present, then ?
zope.cachedescriptors.property.Lazy would work even better:
@Lazy
def b_cache(self):
return PersistentDict()
Marius Gedminas
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