lazy properties?

Stefan H. Holek stefan at
Fri Nov 2 09:36:11 CET 2012

On 01.11.2012, at 22:38, Andrea Crotti wrote:

> Seeing the wonderful "lazy val" in Scala I thought that I should try to get the following also in Python.
> The problem is that I often have this pattern in my code:
> class Sample:
>    def __init__(self):
>        self._var = None
>    @property
>    def var(self):
>        if self._var is None:
>            self._var = long_computation()
>        else:
>            return self._var
> which is quite useful when you have some expensive attribute to compute that is not going to change.
> I was trying to generalize it in a @lazy_property but my attempts so far failed, any help on how I could do that?

There is a ready made and well tested lazy decorator at


Stefan H. Holek
stefan at

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