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

[rusi]

On Dec 23, 7:10 am, alex23 <wuwe... at gmail.com> wrote:
> On Dec 22, 6:51 pm, Rolf Camps <r... at roce.be> wrote:
>
> > I'm afraid it's dangerous to encourage the use of '[]' as assignment to
> > a parameter in a function definition. If you use the function several
> > times 'default' always points to the same list.
>
> I appreciate the concern, but adding a default argument guard would
> not only obscure the code. It's irrelevant, as you recognise, because
> no matter what, it's going to make copies of the default argument.
>
> You know what the say about foolish consistencies :)

Programming languages can have bugs as much as programs can.
A classic example is the precedence table of C which Kernighan or
Ritchie (dont remember which) admitted was wrong.

Likewise function arguments that default to mutable entities is a
known gotcha of python which is best treated as a bug in python. It
should be avoided with the suitable additional circumspection that a
language bug deserves over a program bug.

[Just my rephrasing of what Ian is saying]