Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!news1.tnib.de!feed.news.tnib.de!news.tnib.de!newsfeed.freenet.ag!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <python-python-list@m.gmane.org>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.035
X-Spam-Evidence: '*H*': 0.93; '*S*': 0.00; 'output': 0.05; 'quiet': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:script': 0.09; 'random': 0.14; 'benjamin': 0.16; 'components.': 0.16; 'considers': 0.16; 'does,': 0.16; 'instead:': 0.16; 'kern': 0.16; 'realising': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'storing': 0.16; 'subject:random': 0.16; 'underlying': 0.16; 'wrote:': 0.18; 'thu,': 0.19; '>>>': 0.22; 'header:User-Agent:1': 0.23; 'bytes': 0.24; 'interpret': 0.24; 'mathematical': 0.24; 'typical': 0.24; 'source': 0.25; 'header:X-Complaints-To:1': 0.27; 'header:In- Reply-To:1': 0.27; 'external': 0.29; 'robert': 0.30; "i'm": 0.30; '+0100,': 0.31; '>>>>': 0.31; 'continually': 0.31; "d'aprano": 0.31; 'lot.': 0.31; 'steven': 0.31; 'yes.': 0.31; 'maintaining': 0.32; 'run': 0.32; 'running': 0.33; 'sources': 0.33; 'sense': 0.34; 'could': 0.34; 'but': 0.35; 'really': 0.36; 'accessible': 0.36; 'doing': 0.36; 'operating': 0.37; 'machines': 0.38; 'to:addr :python-list': 0.38; 'generating': 0.39; 'moving': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'called': 0.40; 'how': 0.40; 'even': 0.60; 'is.': 0.60; 'slowly': 0.60; 'numbers': 0.61; 'skip:n 10': 0.64; 'our': 0.64; 'grab': 0.64; 'provide': 0.64; 'world': 0.66; 'believe': 0.68; 'of:': 0.68; 'electrical': 0.74; 'special': 0.74; 'eco': 0.84; 'noise': 0.84; 'oscar': 0.84; 'received:202.71': 0.84; 'subject:long': 0.84; 'terrible': 0.84; 'thermal': 0.84; 'subject:very': 0.91; '2013': 0.98
X-Injected-Via-Gmane: http://gmane.org/
To: python-list@python.org
From: Robert Kern <robert.kern@gmail.com>
Subject: Re: performance of script to write very long lines of random chars
Date: Thu, 11 Apr 2013 19:06:57 +0530
References: <24dc619b-7abd-4be3-aa92-f858eb4ab85f@n4g2000yqj.googlegroups.com> <51666aae$0$29977$c3e8da3$5496439d@news.astraweb.com> <mailman.453.1365673692.3114.python-list@python.org> <51669576$0$29977$c3e8da3$5496439d@news.astraweb.com> <CAHVvXxQmBunWVRL-k8eNv-dM3OzZ2dcg84EbkcdLdfyLgNenxw@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Gmane-NNTP-Posting-Host: 202.71.137.182
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130328 Thunderbird/17.0.5
In-Reply-To: <CAHVvXxQmBunWVRL-k8eNv-dM3OzZ2dcg84EbkcdLdfyLgNenxw@mail.gmail.com>
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <http://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.472.1365687426.3114.python-list@python.org>
Lines: 45
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1365687426 news.xs4all.nl 2634 [2001:888:2000:d::a6]:50807
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:43367

On 2013-04-11 17:35, Oscar Benjamin wrote:
> On 11 April 2013 11:50, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
>> On Thu, 11 Apr 2013 10:47:43 +0100, Oscar Benjamin wrote:
>>
>>> On 11 April 2013 08:47, Steven D'Aprano
>>> <steve+comp.lang.python@pearwood.info> wrote:
>>>
>>>> One thing to be aware of: urandom may run out of entropy, and then it
>>>> will slow down a lot. If you don't care about cryptographic randomness,
>>>> you could use this instead:
>>>
>>> Reading this I'm realising that I don't really know what os.urandom is.
>>> How exactly is it generating random numbers and what do you mean by it
>>> running out of entropy?
>>
>> Some (most?) modern operating systems provide a cryptographically strong
>> source of non-deterministic randomness. The non-deterministic part comes
>> from external "stuff", which is called "entropy". Typical sources of
>> entropy include network events, user key-presses, moving the mouse, and
>> (presumably in machines with special hardware), even thermal noise in
>> electrical components.
>
>> Entropy is used and discarded, so urandom needs the OS to continually
>> replenish the amount of entropy. Under normal circumstances, this it
>> does, but if you grab lots of urandom output on a system which is
>> otherwise quiet and not doing anything, it could run out.
>
> Okay, so I understand what entropy is in the thermodynamic sense and
> also in the mathematical (Shannon) sense but I'm still confused about
> what it means that the OS is somehow storing entropy. Do you mean that
> it is always maintaining a buffer of what it considers to be random
> bytes that it slowly builds up from noise that is made accessible to
> the OS from the hardware?

Yes.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco