[Python-Dev] Re: Proper tail recursion

Christian Tismer tismer at stackless.com
Mon Jul 19 23:17:36 CEST 2004


David Eppstein wrote:

> In article <005701c46db5$764b48d0$6602a8c0 at arkdesktop>,
>  "Andrew Koenig" <ark-mlist at att.net> wrote:
> 
> 
>>>I also haven't seen the use case that requires this and couldn't
>>>easily be fixed by changing the data structure or code slightly.
>>>(Andrew Koenig's theoretical objections don't count as use cases.)
>>
>>Didn't we just hear that this problem affects pickling?
> 
> 
> We heard that the recursion limit prevents recursive DFS from being 
> applied to large graphs, and that pickling uses DFS.  However, tail 
> recursion wouldn't help in this case -- it's a deep recursion but not a 
> tail recursion.

[dropping interesting details for my brute-force solution]

I went a different and very simple path for Stackless:
When cPickle goes too deep, I simply allocate a new C stack
and let it continue. That was the simplest possible patch
for me, since I only wanted it to no longer crash.
Not that this is not needed for unpickling; this structure
is as flat as it can be.

ciao - chris

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