sharing attributes between classes in python

Question

I am not sure how to accomplish something that should be straightforward.

I want to define a class. In that class will be subclasses. In those subclasses will be attributes.

Ok, that's easy. But I want the attributes of one subclass to be generated based on the attributes of another of the subclasses. Here is my (wrong) code to try to do that:

class Food(object):
    class Fruits(object):
        crunchy=['Apples', 'Pears']
        juicy=['Limes', 'Lemons']

    class Salads(object):
        import Fruits
        FruitSalad=crunchy+juicy+['Whipped Cream']

Obviously "import Fruits" is wrong here. But how can I accomplish what I need?

-------------edit/addendum--------------------------------------

Ok, so I lose the outer class "Food", that's ok, I never liked it anyway.

I can now instantiate the first class into the second like this:

class Fruits(object):
    crunchy=['Apples', 'Pears']
    juicy=['Limes', 'Lemons']

class Salads(object):
    fruit=Fruits
    FruitSalad=fruit.crunchy+fruit.juicy+['Whipped Cream']

Which is closer, but I really want to lose the "fruit." structure.

Why are you nesting classes? What are you trying to accomplish? — Martijn Pieters
– Martijn Pieters, Commented Feb 12, 2013 at 15:59
I want to be able to instantiate "Food.Salads" somewhere else. — Skip Huffman
– Skip Huffman, Commented Feb 12, 2013 at 16:00
You do not need to use import Fruits at all. Only use import to import structures from another file. These definitions are in the same file. — Martijn Pieters
– Martijn Pieters, Commented Feb 12, 2013 at 16:00
Why not just create a module named food, then you can do import food and create an instance of food.Salads(). — Martijn Pieters
– Martijn Pieters, Commented Feb 12, 2013 at 16:01
Yeah, I realize it is wrong. I put it there to illustrate what I was trying to do. — Skip Huffman
– Skip Huffman, Commented Feb 12, 2013 at 16:01

engineerC · Accepted Answer · 2013-02-12 16:14:05Z

3

Perhaps there is some confusion about subclasses vs. encapsulation. Here is an example hierarchy if you're looking for inheritance. Note that this particular code is not making much use of the hierarchy and just some bare lists would be easier, and the variables are all class variables, not per-instance.

class Food(object):
    pass

class Fruit(Food):
    pass

class Salad(Food):
    pass

class CrunchyFruit(Fruit):
    ingredients = ['apples','pears']

class JuicyFruit(Fruit):
    ingredients = ['limes','lemons']

class FruitSalad(Salad):
    ingredients = JuicyFruit.ingredients + CrunchyFruit.ingredients + ['whipped cream']

print(FruitSalad.ingredients)

answered Feb 12, 2013 at 16:14

engineerC

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Comments

Martijn Pieters · Accepted Answer · 2013-02-12 16:28:44Z

1

Because you are defining this as a nested set of classes, you are needlessly complicating things. The explanation is now going to involve words like "class suite" and why you'd need Fruits.crunchy in one place and Food.Fruits.crunchy in another. You are also trying to concatenate lists and a string, which won't work.

Just keep things simple, create a module named food, then you can do import food and create an instance of food.Salads().

answered Feb 12, 2013 at 16:28

Martijn Pieters

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