[Tutor] How to access an instance variable of a superclass from an instance of the subclass?
boB Stepp
robertvstepp at gmail.com
Wed Feb 22 23:53:03 EST 2017
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
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