Path: csiph.com!usenet.pasdenom.info!news.redatomik.org!newsfeed.xs4all.nl!newsfeed1a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
In-Reply-To: <CAPTjJmqmVuFmZbhtiiOj2haVjFuHOYrBVcNLSe6ohUUS1btNBA@mail.gmail.com>
References: <87mw1q9jqw.fsf@Equus.decebal.nl> <mailman.121.1430385051.3680.python-list@python.org> <87383hj4zj.fsf@elektro.pacujo.net> <87d22lx38x.fsf@Equus.decebal.nl> <55432557$0$12994$c3e8da3$5496439d@news.astraweb.com> <87383fo062.fsf@Equus.decebal.nl> <87egmzl4yr.fsf@elektro.pacujo.net> <mailman.4.1430558719.12865.python-list@python.org> <87a8xnl2r6.fsf@elektro.pacujo.net> <mi2b49$pip$1@dont-email.me> <mailman.9.1430565706.12865.python-list@python.org> <mi2cjc$uq2$1@dont-email.me> <87383fkxy0.fsf@elektro.pacujo.net> <CALwzidn_4EyKA-AekPqwk2+1+0Yd3ONsTdKx73bfpzZkyXj++w@mail.gmail.com> <CAPTjJmqmVuFmZbhtiiOj2haVjFuHOYrBVcNLSe6ohUUS1btNBA@mail.gmail.com>
From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Sat, 2 May 2015 11:00:04 -0600
Subject: Re: Python is not bad ;-)
To: Python <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.19.1430586047.12865.python-list@python.org>
Lines: 29
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:89782

On Sat, May 2, 2015 at 9:55 AM, Chris Angelico <rosuav@gmail.com> wrote:
> On Sun, May 3, 2015 at 1:45 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>> On Sat, May 2, 2015 at 5:42 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>>> Christian Gollwitzer <auriocus@gmx.de>:
>>>
>>>> That's why I still think it is a microoptimization, which helps only
>>>> in some specific cases.
>>>
>>> It isn't done for performance. It's done to avoid a stack overflow
>>> exception.
>>
>> If your tree is balanced, then the number of items you would need to
>> have to get a stack overflow exception would be approximately 2 **
>> 1000, which you can't possibly hope to fit into memory.
>>
>> If your tree is unbalanced and you're getting a stack overflow
>> exception, then maybe you should think about balancing it.
>
> That's assuming it's a search tree, where you *can* just "think about
> balancing it". What if it's a parse tree? Let's say you're walking the
> AST of a Python module, looking for all functions that contain 'yield'
> or 'yield from' (ie generator functions). To do that, you need to walk
> the entire depth of the tree, no matter how far that goes. I'm not
> sure how complex a piece of code would have to be to hit 1000, but it
> wouldn't be hard to have each level of tree cost you two or three
> stack entries, so that could come down to just a few hundred.

Or you just iterate over the ast.walk generator, which uses a deque
rather than recursion.