John Posner a écrit :
On 3/22/2010 11:44 AM, Bruno Desthuilliers wrote:
<snip>
Another (better IMHO) solution is to use a plain property, and store the
computed value as an implementation attribute :
@property
def foo(self):
cached = self.__dict__.get('_foo_cache')
if cached is None:
self._foo_cache = cached = self._some_time_consuming_operation()
return cached
There's no need to access __dict__ directly.
Nope, inded. I guess I wrote it that way to make clear that we were
looking for an instance attribute (as a sequel of my previous writing on
attribute lookup rules).
I believe this is
equivalent (and clearer):
@property
def foo(self):
try:
cached = self._foo_cache
except AttributeError:
self._foo_cache = cached = self._time_consuming_op()
return cached
This is functionally _almost_ equivalent - won't work the same if
there's a class attribute "_foo_cache", which might or not be a good
thing !-)
Will possibly be a bit faster after the first access - IIRC setting up
an error handler is by itself cheaper than doing a couple attribute
access and a method call - but I'd timeit before worrying about it.
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