Nested Classes and Instances

[J. Cliff Dyer]

On Fri, 2009-07-10 at 19:00 +0200, Manuel Graune wrote:
> Hello,
> 
> as an example of what I would like to achieve, think of a street
> where each house has a door and a sign with a unique (per house)
> number on it. I tried to model this like this:
> 
> class House(object):
>     class Door(object):
>         def __init__(self,color):
>              self.color=color
>     class Sign(object):
>         def __init__(self,text):
>              self.text=text
>     def __init__(self, doorcolor,housenumber):
>         self.housenumber=housenumber
>         self.door=House.Door(doorcolor)
>         self.sign=House.Sign(housenumber)
> 
> house1=House("red","1")
> house2=House("blue","2")
> 

Don't do it like that.  Keep your classes independent.  Many houses can
have doors, and there's no reason to redefine the concept of Doors for
each one.  Same goes for Signs.  

class House(object):
    def __init__(self, doorcolor, housenumber):
        self.door = Door(doorcolor)
        self.sign = Sign(housenumber)
        self.number = housenumber

class Door(object):
    def __init__(self, color):
        self.color = color

class Sign(object):
    def __init__(self, inscription):
        self.inscription = str(housenumber)



(Something like that)

Cheers,
Cliff




> Well, so far, so good. Now, what I'd like to achive is that the text of
> the "sign" changes whenever the variable "housenumber" of the
> "parent-instance" changes or  that
> "house1.sign.text" is a reference/pointer to "house1.housenumber"
> 
> Thanks in advance,
> 
> Manuel
> 
> 
> 
> -- 
> A hundred men did the rational thing. The sum of those rational choices was
> called panic. Neal Stephenson -- System of the world
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