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

[Mikolaj Antoszkiewicz]

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.

Mikolaj

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