On Thu, Sep 20, 2012 at 12:25 PM, eryksun <eryk...@gmail.com> wrote:
>
> cls._count += 1
I forgot the obligatory warning about class variables. The subclass
gets a shallow copy of the parent class namespace. The in-place
addition above works because numbers are immutable. However, an
in-place operation on a mutable object would modify the value shared
by the parent and all other subclasses.
Simple example:
>>> class X(object): data = []
>>> class Y(X): pass
>>> Y.data += [1]
>>> X.data # modified parent, too
[1]
But rebinding the attribute name is OK:
>>> Y.data = Y.data + [2] # creates new list
>>> Y.data
[1, 2]
>>> X.data
[1]
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