[Tutor] Populating a list with object to be called by a class
Steven D'Aprano
steve at pearwood.info
Thu Sep 20 21:56:46 CEST 2012
On 21/09/12 03:18, eryksun wrote:
> On Thu, Sep 20, 2012 at 12:57 PM, eryksun<eryksun at gmail.com> wrote:
>>
>> I forgot the obligatory warning about class variables. The subclass
>> gets a shallow copy of the parent class namespace. The in-place
> ^^^^^^^^^^^^^^^^^^^
>> >>> Y.data += [1]
>> >>> X.data # modified parent, too
>> [1]
>> >>> Y.data = Y.data + [2] # creates new list
>
> To clarify, it's not an actual dict.copy in the subclass.
Ah, I didn't notice you had corrected yourself before sending my
own correction.
> In fact, the
> atrribute is initially only in the parent __dict__, where it's found
> by object.__getattribute__. In the 2nd example, Y.data on the
> right-hand side is actually found in the parent class X, then the
> expression creates a new list which is stored back to Y.
Pretty much.
Inheritance couldn't work correctly if subclasses made copies of their
parent namespaces.
--
Steven
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