what does 'a=b=c=[]' do

[Eric]

On Dec 21, 6:50 pm, alex23 <wuwe... at gmail.com> wrote:
> On Dec 22, 8:25 am, Eric <einazaki... at yahoo.com> wrote:
>
> > This surprises me, can someone tell me why it shouldn't?  I figure if
> > I want to create and initialize three scalars the just do "a=b=c=7",
> > for example, so why not extend it to arrays.
>
> The thing to remember is that everything is an object, and that it's
> better to think of variables as labels on an object.
>
> So: a=b=c=7 means that _one_ integer object with the value of 7 can be
> referenced using any of the labels a, b or c. x=y=z=[] means that
> _one_ empty list can be referenced using x, y or z.
>
> The difference is that the value of a number object _cannot be
> changed_ ('immutable') while a list can be modified to add or remove
> items ('mutable'). a=10 just reassigns the label a to an integer
> object of value 10. x.append("foo") _modifies_ the list referred to by
> x, which is the same list known as y & z.
>


> > Also, is there a more pythonic way to do "x=[], y=[], z=[]"?
>
> I'd say that _is_ the most pythonic way, it's very obvious in its
> intent (or would be with appropriate names). If it bothers you that
> much:
>

Thanks for the explanation.  I guess from what I've seen of Python
so far I was expecting something more, I don't know, compact.
Anyway, it doesn't bother me, at least not enough to go and do
something like this:

>     def listgen(count, default=[]):
>         for _ in xrange(count):
>             yield default[:]
>
>     x, y, z = listgen(3)

Thanks,
eric