CODEWITHSUNDEEP
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Juliusz Gonera
Juliusz Gonera

Reputation: 4958

Accessing a child class from another child class inside parent class

I really didn't know what title I should choose. Anyway, I have code like this (this is fixtures):

from fixture import DataSet

class CategoryData(DataSet):
    class cat1:
        name = 'Category 1'
    class cat2:
        name = 'Category 2'
        parent = cat1

The problem is I can't reference cat1 in cat2 like that:

File "/home/julas/cgp/cgp/datasets/__init__.py", line 11, in cat2
    parent = cat1
NameError: name 'cat1' is not defined

How can I do it?

Upvotes: 1

Views: 268

Answers (2)

Glenn Maynard
Glenn Maynard

Reputation: 57474

There are two problems here.

First, Python doesn't do nested scoping like that for you. To access CategoryData.cat1, you need to spell it out.

Second, and a bigger issue, is that there's no way to access CategoryData from there: the class hasn't been defined yet, since you're in the middle of defining it. If you do this:

class Object(object):
    a = 1
    b = Object.a

it'll fail, because the value of Object isn't assigned until the end of the class definition. You can think of it as happening like this:

class _unnamed_class(object):
    a = 1
    b = Object.a
Object = _unnamed_class

There's no way to reference a from where b is assigned, because the containing class hasn't yet been assigned its name.

In order to assign parent as a class property, you need to assign it after the containing class actually exists:

class CategoryData(DataSet):
    class cat1:
        name = 'Category 1'
    class cat2:
        name = 'Category 2'
CategoryData.cat2.parent = CategoryData.cat1

Upvotes: 3

vonPetrushev
vonPetrushev

Reputation: 5599

You either: Move it out of the definition:

CategoryData.cat2.parent=CategoryData.cat1

Or, if it's an object attribute (and not a class attribute):

class cat2:
    name = 'Category 2'
    def __init__(self):
        self.parent = cat1

Upvotes: 1

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