a little bit of recursion

[Gregor Lingl]

rzed schrieb:
> Dominik Kaspar wrote:
> 
>>I'm trying to write a quite big recursive function, but the baseline
>>is the following:
>>
>>def rek(N, L):
>>    N = N + 1
>>    if N >= 9: return L
>>    else: return rek(N, L = L.append(N))
>>
>>print rek(0, [])
>>
>>Why isn't this working?
>>In my opinion it should return [1, 2, ..., 9]
>>
>>Thanks for any answers.
> 
> 
> 
> One problem is that L = L.append(N) does not have the effect you want.
> Try it on its own.
> Another is that it won't return [1,2,...,9] even when that is
> corrected.

That certainly depends on the way one corrects it.
However Dominik first has to notice, that append is a
method, which *changes* L but doesn't return L. Instead
it returns None. So it may be ok to call L.append(N),
but not on the right side of an assignment statement.

You can obsrve what I mean here:

 >>> L = [1,2,3]
 >>> print L.append(4)
None
 >>> L
[1, 2, 3, 4]
 >>>

HTH, Gregor
> 
> 
> 
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