[Tutor] Populating a list with object to be called by a class
eryksun
eryksun at gmail.com
Thu Sep 20 19:18:58 CEST 2012
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. 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.
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