Inheritance inside Classes Python3

Question

I need something like this

class Parent(object): 
    class Base(object):
        def __init__(self, a, b):
            self.a = a
            self.b = b


    class Derived(Base):
        def __init__(self, a, b, c):
            super(Derived,self).__init__(a, b)
            self.c = c

        def doit():
            pass

parent = Parent()
derived = parent.Derived(x,y,z)
derived.doit()

When I try to run this, i get this following error: NameError: name 'Derived' is not defined

I tried with 'Base' in the place of 'Derived' in super() - didn't help

Why would you want to do this? What's the point of that nesting? — Daniel Roseman
– Daniel Roseman, Commented Apr 17, 2015 at 13:43
Would it not just be better to declare Derived inside of Parent? — Nafiul Islam
– Nafiul Islam, Commented Apr 17, 2015 at 13:46
what python version are you running? is it not enough to go with super().__init__ ? — user3012759
– user3012759, Commented Apr 17, 2015 at 13:48
You are trying to call Derived inside the Parent class, wich doesn't exist, and you get the NameError. What are you trying to achieve? — CoMartel
– CoMartel, Commented Apr 17, 2015 at 13:49
@daniel: the 'Derived' object should not exist without a 'Parent' object. A remotely similar example is 'Note' written in a paper, cannot exist without 'Paper' object. — vanangamudi
– vanangamudi, Commented Apr 19, 2015 at 16:17

rth · Accepted Answer · 2015-04-17 13:48:55Z

2

Class inheritance does not change the parent class. In this case your Parent class only contains the original Base class and not the derived class.

You can simply use monkey-patching to solve this problem,

class Parent(object): 
    pass


class Base(object):
    def __init__(self, a, b):
        self.a = a
        self.b = b


class Derived(Base):
    def __init__(self, a, b, c):
        super(Derived,self).__init__(a, b)
        self.c = c

    def doit(self):
        pass

Parent.Derived = Derived

parent = Parent()
x, y , z = 1, 1, 1
derived = parent.Derived(x,y,z)
derived.doit()

answered Apr 17, 2015 at 13:48

rth

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Comments

vanangamudi · Accepted Answer · 2015-04-20 07:16:05Z

0

Prefixing 'Derived' with 'Parent.', made it. As I already have commented on the question. This is just for experimenting with the 'Derived' class. But I am still wondering how the, 'class Derived(Base):' is fine (without 'Parent.' prefix for 'Base' class)

class Parent(object): 
    class Base(object):
        def __init__(self, a, b):
            self.a = a
            self.b = b


    class Derived(Base):
        def __init__(self, a, b, c):
            super(Parent.Derived,self).__init__(a, b)
            self.c = c

        def doit():
            pass

parent = Parent()
derived = parent.Derived(x,y,z)
derived.doit()

answered Apr 20, 2015 at 7:16

vanangamudi

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