[Tutor] How to access an instance variable of a superclass from an instance of the subclass?

[boB Stepp]

On Wed, Feb 22, 2017 at 10:25 PM, boB Stepp <robertvstepp at gmail.com> wrote:
> I am trying to wrap my head around the mechanics of inheritance in
> Python 3.  I thought that all attributes of a superclass were
> accessible to an instance of a subclass.  But when I try the
> following:
>
> py3: class A:
> ...     def __init__(self):
> ...             self.aa = 'class A'
> ...
> py3: class B(A):
> ...     def __init__(self):
> ...             self.bb = 'class B'
> ...
> py3: a = A()
> py3: b = B()
> py3: b.aa
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: 'B' object has no attribute 'aa'
>
> I am unsuccessful...

I have partially answered my own question, but I am not sure I
understand the mechanics yet.  Apparently I must explicitly assign
class A's attribute, aa, to an instance of class B as follows:

py3: class B(A):
...     def __init__(self):
...             self.aa = super().aa
...             self.bb = 'class B'
...
py3: b = B()
py3: b.aa
'class A'

I was expecting that all of A's methods and attributes would
seamlessly be available to any instance of class B, but apparently
this is wrong-headed on my part.  Instead, it looks like I need to
explicitly attach A's methods and attributes to B's instances via B's
self.

I will continue to mull this over.

-- 
boB