Default list parameter issue

[Olivier Boudeville]

Oh, thanks a lot Peter, I did not know about it and was totally stuck.

IMHO, this 'feature' is counter-intuitive. Maybe it allows to write in 
some cases simplier or more efficient functions, but there are enough 
traps not to add more of them, with this kind of side-effects.

I believed, with filter, list comprehension and so on, that python was 
making some steps towards 'functional programming' and declarative 
languages (sorry if the translations are not accurate). It would have 
led to more robust code. It is certainly not that way that recursive 
functions will be easy to write and understand (but it is just my 
opinion) !

I do not find/wish this behaviour is 'pythonic', but of course it is a 
matter of taste.

Thanks again nevertheless, it helped me a lot !

Olivier.


Peter Otten wrote:
> Olivier Boudeville wrote:
> 
> 
>>I do not understand why using an empty list as default parameter results
>>  in such a different behaviour.
> 
> 
> You are not alone.
> 
> http://www.python.org/doc/faq/general.html#why-are-default-values-shared-between-objects
> 
> Peter