Daniel Fetchinson schrieb:
> Hi list, I've been following a discussion on a new way of defining
> getters and setters on python-dev and just can't understand what the
> purpose is. Everybody agreed on the dev list that this is a good idea
> so I guess it must be right :)
>
> The whole thing started with this post of Guido:
>
> http://mail.python.org/pipermail/python-dev/2007-October/075057.html
>
> which then continued into November. Basically, the idea is that using
> the new way a setter can be added to property that was read-only
> before. But if I have this already,
>
> class C:
> @property
> def attr( self ): return self._attr
>
> what prevents me using the following for adding a setter for attr:
>
> class C:
> def attr( self ): return self._attr
> def set_attr( self, value ): self._attr = value
> attr = property( attr, set_attr )
>
> In other words all I needed to do is delete @property, write the
> setter method and add attr = property( attr, set_attr ). What does the
> new way improve on this?
It prevents namespace-pollution in a clever way. By first defining the
getter, the @propset-decorator will augment the already createt property
and return it.
Thus you don't end up with a
set_attr
function.
Other, more complex recipes to do the same look like this and are much
harder to grasp:
@apply
def my_property()
def fget(self):
return self._value
def fset(self, value):
self._value = value
return property(**locals())
So the proposed propset-decorator certainly makes things clearer.
Diez
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