Default Value

[Roy Smith]

In article <51c39b88$0$29999$c3e8da3$5496439d at news.astraweb.com>,
 Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:

> On Thu, 20 Jun 2013 09:19:48 -0400, Roy Smith wrote:
> 
> > In article
> > <447dd1c6-1bb2-4276-a109-78d7a067b442 at d8g2000pbe.googlegroups.com>,
> >  rusi <rustompmody at gmail.com> wrote:
> > 
> >> > > def f(a, L=[]):
> >> > > Â  Â  L.append(a)
> >> > > Â  Â  return L
> > 
> >> Every language has gotchas. This is one of python's.
> > 
> > One of our pre-interview screening questions for Python programmers at
> > Songza is about this.  I haven't been keeping careful statistics, but
> > I'd guess only about 50% of the candidates get this right.
> 
> 
> What exactly is the question? Because it's not always a bug to use a 
> mutable default, there are good uses for it:

It's a screening question; I'd rather not reveal all the details (it's 
really annoying when you find your screening questions posted to stack 
overflow).  But, yes, I understand that there are good uses.