'Once' properties.

Carl Banks pavlovevidence at gmail.com
Tue Oct 6 08:12:46 CEST 2009

On Oct 5, 11:07 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
> On Oct 5, 7:56 pm, menomnon <p... at well.com> wrote:
> > Does python have a ‘once’ (per class) feature?
> > ‘Once’, as I’ve know it is in Eiffel.  May be in Java don’t.
> > The first time you instantiate a given class into an object it
> > constructs, say, a dictionary containing static information.  In my
> > case static is information that may change once a week at the most and
> > there’s no need to be refreshing this data during a single running of
> > the program (currently maybe 30 minutes).
> > So you instantiate the same class into a second object, but instead of
> > going to the databases again and recreating the same dictionary a
> > second time, you get a pointer or reference to the one already created
> > in the first object – copies into the second object that is.  And the
> > dictionary, no matter how many instances of the object you make, is
> > always the same one from the first object.
> > So, as we put it, once per class and not object.
> > Saves on both time and space.
> Sounds like Borg Pattern:
> http://code.activestate.com/recipes/66531/

BTW, for your problem you'd probably want to add some kind of
conditional initialization code:

class Borg(object):
    _shared_state = { 'initialized' : False }

    def __init__(self):
        self.__dict__ = self._shared_state
        if self.initialized:
        # perform initialization here
        self.initialized = True

Carl Banks

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