On Monday 17 January 2005 20:55, Frans Englich wrote:
> On Monday 17 January 2005 19:02, Peter Otten wrote:
> > Frans Englich wrote:
> > > What the code attempts to do is implementing a, to the API user,
> > > transparent memory-saver by ensuring that no more than one instance of
> > > the class foo exists for a particular id. E.g, the user can simply
> > > "create" an instance and if one not already exists, it is created.
> >
> > By the time __init__() is called, a new Foo instance has already been
> >
> > created. Therefore you need to implement Foo.__new__(). E. g.:
> > >>> class Foo(object):
> >
> > ... cache = {}
> > ... def __new__(cls, id):
> > ... try:
> > ... return cls.cache[id]
> > ... except KeyError:
> > ... pass
> > ... cls.cache[id] = result = object.__new__(cls, id)
> > ... return result
> > ... def __init__(self, id):
> > ... self.id = id
> > ... def __repr__(self):
> > ... return "Foo(id=%r)" % self.id
> > ...
>
> I'm not sure, but I think this code misses one thing: that __init__ is
> called each time __new__ returns it, as per the docs Peter posted.
Ahem, John I ment :)
The second typo today..
Cheers,
Frans
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