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.
Cheers,
Frans
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