[Tutor] function local var problem :-((

[Lloyd Kvam]

A good site that lists some other Python pitfalls:

http://zephyrfalcon.org/labs/python_pitfalls.html
zephyrfalcon.org :: labs :: 10 Python pitfalls

#5 is using a mutable variable as a function default.

mjekl at clix.pt wrote:

> Hi,
> 
> I'm new here and with programming. I've been learning on my own and cannot
> understand what happens with this function I created.
> 
> The function is in it's own module that I import into shell.
> 
> ###### module1.py ######
> 
> def printHierarchy(objecto, printList=[]):
>    """Prints a class hierarchy given an object.
>       Works only with single inheritance hierarchies."""
> 
>    if objecto.__class__.__bases__:
>       printList.append(objecto.__class__.__name__)
>       recurObjecto = objecto.__class__.__bases__[0]()
>       return printHierarchy(recurObjecto, printList)
>    else:
>       printList.append(objecto.__class__.__name__)
> 
>       if not objecto.__class__.__bases__:
> 	 i = 0
> 	 for klass in printList:
> 	    print i * ' ' + klass
> 	    i += 1
>       else:
> 	 return printList
> 
> ####################
> 
> in shell I created a hierarchy of three classes:
> class Sup; class Sub1(Sup); class Sub2(Sub1)
> 
> Then:
> 
>>>>oSub2 = Sub2()
>>>>printHierarchy(oSub2)
> 
> Sup
>    Sub1
>       Sub2
> 
> 
> The problem is that if I call the function again I get:
> 
>>>>printHierarchy(oSub2)
> 
> Sup
>    Sub1
>       Sub2
> 	 Sup
> 	    Sub1
> 	       Sub2
> 
> 
> The problem to me is that I think that the var printList is local and that
> it is initialized every time the function is called. But results contradict
> this assumption. So I tried to investigate the namespaces and found no
> references to var printList. I guess my investigation is bad (In shell I
> issued dir() and dir(module1)
> and got nothing. Also tried to use:
>  from module1 import printHierarchy
> But didn't work either. Can someone please help me?
> 
> Python 2.2 winXP
> 
> Txs,
> Miguel
> 
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-- 
Lloyd Kvam
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