[Erp5-dev] Default parameter (list) [eg] in OrderBuilder - which way is better?

[Łukasz Nowak]

Hello,

On 2008-06-12, 10:54:18
Mikolaj Antoszkiewicz <mikolaj at erp5.pl> wrote:

> 
> 
> Łukasz Nowak wrote:
> > Hello,
> > 
> > If list is passed as optional argument, its defaults shall be None
> > or []?
> > 
> > Take for example ERP5/Document/OrderBuilder.py - everywhere
> > foo_list on method argument list has defaults to None. Without
> > proper initialisation there are problems, if method is called
> > without changing parameter to empty list eg.
> > 
> > Which is more correct:
> > 
> > def funA(self, movement_list=None):
> >   if movement_list is None:
> >     movement_list = []
> >   =snip=
> > 
> > def funB(self, movement_list=[]):
> >   =snip=
> > 
> > ?
> > 
> In general, it's not desirable to use unmutables as default
> parameters. They behave differently than usually expected to
> (consequent calls to that function will work on existing list, not on
> a new empty one as one might expect)
> That's why funB type should be used only if You know what You're
> doing and You want that.

unmutable is immutable? list ([]) is not immutable, isn't it? So this
is not that issue? Or I got something wrong? (Now I'm quite confused.)

But ok. So the error, is that those variables wasn't changed to list if
None was passed?

Regards,
Luke

-- 
Łukasz Nowak R&D Ventis http://www.ventis.com.pl/
tel: +48 32 768 16 85 fax: +48 32 392 10 61
``Use the Source, Luke...'' I am only craftsman.