[Python-Dev] [ python-Patches-876206 ] scary frame speed hacks (original) (raw)

Michael Hudson mwh at python.net
Tue Mar 2 12:26:56 EST 2004

Jeremy Hylton <jeremy at alum.mit.edu> writes:

On Tue, 2004-03-02 at 12:17, Bob Ippolito wrote:

Well it's already true to some small extent because of the recursion depth limit. Though, this has only been a problem for me once, and I rewrote it as a large ugly iterative version. Don't know the particulars, but I thought it worth mentioning that the recursion limit is set fairly conservatively. In many cases, it's possible to boost the recursion limit. I don't know if it's ever practical, because if something goes wrong you get a segfault. Different kinds of recursive Python calls generated different numbers of C stack frames. So if you have a recursive repr(), it will consume more C stack than a simple Python function. Python's recursion limit is set to 1000 in 2.3. On my box (RH9) the first crash I get is with a recursion limit of 5800. It blows up on the repr case. For simple recursive functions, I can push it all the way up to 21,500.

But list_sort pushes quite a large object onto the stack. So if you arrange for that too appear on the stack repeatedly, you get a crash much earlier.

Python's recursion limit is a nasty hack. Unfortunately, all the alternatives are worse :-( (except some variant of stackless, I guess, but that probably doesn't help the list_sort business).

Cheers, mwh

-- I have a cat, so I know that when she digs her very sharp claws into my chest or stomach it's really a sign of affection, but I don't see any reason for programming languages to show affection with pain. -- Erik Naggum, comp.lang.lisp

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