Vincent Gulinao wrote:
> Sorry about that. I want something like:
>
> class foo:
>
> def __init__(self):
>
> self.attr1 = None
>
>
> def get_attr1(self):
>
> if not self.attr1:
>
> attr1 = <get value from DB, very expensive query>
>
> self.attr1 = attr1
>
> return self.attr1
>
>
> such that:
>
> foo_instance = foo()
>
> then:
>
> foo_instance.get_attr1()
>
> and
>
> foo_instance.attr1
>
> gets the same value.
>
>
> Such that you get to derive attr1 only as needed and just once, both
> outside and within foo class.
I would do it like this:
class Foo(object):
def __getattr__(self, attr):
if not <attr is something you can get from the database>:
raise AttributeError(
"'%s' object has no attribute '%s'" %
(self.__class__.__name__, attr))
value = <get attr from database>
setattr(self, attr, value)
return value
You don't need to init attr1 and you don't need get_attr1().
The first time you try to read foo.attr1, there will be no attr1
attribute so __getattr(self, 'attr1') will be called. You read the value
from the database and save it as an ordinary attribute; future accesses
will read the ordinary attribute and skip the __getattr__() call.
Kent
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