[Tutor] beginner: using optional agument in __init__ breaks my code

[Barbara Schneider]

--- Karl Pflästerer <khp at pflaesterer.de> schrieb:

> 
> The values of optional arguments are only once
> evaluated (when Python
> reads the definition). If you place there mutable
> objects like e.g. a
> list most of the time the effect you see is not what
> you want. So you
> have to write it a bit different.
> 
>      def __init__(self, q = None):
>          if not q: q = []
>          self.queue = q
> 
> or
> 
>      def __init__(self, q = None):
>          self.queue = q or []
> 
> Now you get a fresh list for each instance.
> 
>    Karl

Thank you very much. I will use your code as a
"recipe", while I still try to understand the
mechanism and the reasons behind it. For me this feels
odd.  

Barb




	

	
		
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