Jeremy Sanders wrote:
> Is it possible to implement some sort of "lazy" creation of objects only
> when the object is used, but behaving in the same way as the object?
>
> For instance:
>
> class Foo:
> def __init__(self, val):
> """This is really slow."""
> self.num = val
>
> # this doesn't call Foo.__init__ yet
> a = lazyclass(Foo, 6)
>
> # Foo is only initalised here
> print a.num
>
> What I really want to do is make an object which looks like a numarray,
> but only computes its contents the first time it is used.
Almost anything is possible in Python, though whether the underlying
design idea is sound is a completely different question. (Translation:
try the following pseudo-code, but I have my suspicions about whether
what you're doing is a good idea. :-) )
class lazyclass(object):
'''should probably be called lazyobject though...'''
def __init__(self, class_, *args, **kwargs):
self.class_ = class_
self.args = args
self.kwargs = kwargs
self.obj = None
def _getnum(self):
if self.obj is None:
self.obj = self.class_(*args, **kwargs)
return self.obj.num
num = property(_getnum)
Now that "should" do precisely what you've asked for above, though it is
obviously very limited in supporting only a single attribute name even
though the __init__ method is somewhat generalized. I didn't try
testing the code so there could be typos.
-Peter
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