Le Wednesday 03 September 2008 15:57:50 mk, vous avez écrit :
> I try to set two properties, "value" and "square" in the following code,
> and arrange it in such way that setting one property also sets another
> one and vice versa. But the code seems to get Python into infinite loop:
>
> >>> import math
> >>> class Squared2(object):
>
> def __init__(self, val):
> self._internalval=val
> self.square=pow(self._internalval,2)
>
> def fgetvalue(self):
> return self._internalval
>
> def fsetvalue(self, val):
> self._internalval=val
> self.square=pow(self._internalval,2)
>
> value = property(fgetvalue, fsetvalue)
>
> def fgetsquare(self):
> return self.square
> def fsetsquare(self,s):
> self.square = s
> self.value = math.sqrt(self.square)
>
> square = property(fgetsquare, fsetsquare)
>
>
> >>> a=Squared2(5)
>
> Traceback (most recent call last):
> File "<pyshell#11>", line 1, in <module>
> a=Squared2(5)
> File "<pyshell#10>", line 5, in __init__
> self.square=pow(self._internalval,2)
> File "<pyshell#10>", line 19, in fsetsquare
> self.square = s
> File "<pyshell#10>", line 19, in fsetsquare
> self.square = s
> File "<pyshell#10>", line 19, in fsetsquare
> self.square = s
> File "<pyshell#10>", line 19, in fsetsquare
> self.square = s
> File "<pyshell#10>", line 19, in fsetsquare
> self.square = s
> File "<pyshell#10>", line 19, in fsetsquare
>
> ...
>
> Is there a way to achieve this goal of two mutually setting properties?
Your square property is not correctly defined, it recurselively call itself,
it should be (I also avoided the extra lookup) :
def fgetsquare(self):
return self._square
def fsetsquare(self,s):
self._square = s
self.value = math.sqrt(s)
then the fsetvalue will be also be called recursively as it use the square
property, you should also write it :
def fsetvalue(self, val):
self._internalval=val
self._square=pow(val,2)
*but*, if you want to add more logic in the setters, you could want to add two
extra methods :
def _setsquare(self, v) :
# some extra logic here
self._square = s
def fsetsquare(self,s):
self._setsquare(s)
self._setvalue = math.sqrt(s)
def _setvalue(self, val):
# some extra logic here
self._internalval=val
def fsetvalue(self, val):
self._setvalue(val)
self._setsquare=pow(val,2)
Note that if one property can really be computed from another, this kind of
thing could be considered as bad design (except if the computation is heavy).
--
_____________
Maric Michaud
--
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