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From: Ethan Furman on 18 May 2010 17:19
Vincent Davis wrote:
> Lets say I have
> class foo(object):
> def __init__(self, x, y):
> self.x=x
> self.y=y
> def xplusy(self):
> self.xy = x+y
^ this needs to be self.x + self.y
>
> inst = foo(1,2)
> inst.xy # no value, but I what this to cause the calculation of inst.xy
>
> I don't what to have self.xy calculated before it is called.

My current favorite method:

def __getattr__(self, name):
if name != 'xy':
raise AttributeError("%s not found" % name)
self.xy = self.x + self.y
return self.xy


~Ethan~
From: Ethan Furman on 18 May 2010 18:26
Ethan Furman wrote:
> Vincent Davis wrote:
>> Lets say I have class foo(object):
>> def __init__(self, x, y):
>> self.x=x
>> self.y=y
>> def xplusy(self):
>> self.xy = x+y
> ^ this needs to be self.x + self.y
>>
>> inst = foo(1,2)
>> inst.xy # no value, but I what this to cause the calculation of inst.xy
>>
>> I don't what to have self.xy calculated before it is called.
>
> My current favorite method:
>
> def __getattr__(self, name):
> if name != 'xy':
> raise AttributeError("%s not found" % name)
> self.xy = self.x + self.y
> return self.xy
>
>
> ~Ethan~

Chris' reply is more on-point, I think -- I was thinking of attributes
that are only calculated once. *sigh*

~Ethan~
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