Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.kamp.net!newsfeed.kamp.net!feeder1.cambriumusenet.nl!feed.tweaknews.nl!194.109.133.86.MISMATCH!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!news.tele.dk!news.tele.dk!small.news.tele.dk!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.005 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'algorithm': 0.04; 'memory.': 0.07; 'modified': 0.07; 'computed': 0.09; 'friday,': 0.09; 'lines.': 0.09; 'python:': 0.09; 'referenced': 0.09; 'statements': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; '(assuming': 0.16; 'comments:': 0.16; 'relevant.': 0.16; 'sure.': 0.16; 'variable.': 0.16; '\xc2\xa0i': 0.16; '\xc2\xa0if': 0.16; 'wrote:': 0.18; 'code.': 0.18; 'looked': 0.18; '<': 0.19; '>>>': 0.22; 'example': 0.22; 'python?': 0.22; 'cc:addr:python.org': 0.22; '>>>': 0.24; 'cc:2**0': 0.24; '>': 0.26; 'references': 0.26; 'this:': 0.26; 'second': 0.26; 'read,': 0.26; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'am,': 0.29; 'dec': 0.30; 'robert': 0.30; 'start,': 0.30; 'message-id:@mail.gmail.com': 0.30; 'url:mailman': 0.30; 'code': 0.31; 'lines': 0.31; "skip:' 10": 0.31; 'url:wiki': 0.31; 'end,': 0.31; 'subject:some': 0.31; 'url:wikipedia': 0.31; 'quite': 0.32; 'url:python': 0.33; 'fri,': 0.33; 'implemented': 0.33; 'minimal': 0.33; 'december': 0.35; 'operations': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'there': 0.35; 'really': 0.36; 'described': 0.36; 'false': 0.36; 'largely': 0.36; 'url:listinfo': 0.36; 'url:org': 0.36; 'two': 0.37; 'performance': 0.37; 'skip:& 10': 0.38; 'url:mail': 0.40; 'how': 0.40; 'read': 0.60; 'algorithms': 0.60; 'john': 0.61; 'simple': 0.61; 'discuss': 0.62; 'more': 0.64; 'benefit': 0.68; 'deeply': 0.69; 'below.': 0.71; 'completely,': 0.84; 'draws': 0.84; 'raster': 0.84; 'old,': 0.85; 'joel': 0.91; 'write:': 0.91; '2013': 0.98 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=e8Xgq01bXUMK1P69icPH5yFdbHyYWtvVDfPAj5EyxK4=; b=n/scXAPEL9G/k3rRDn1AvYeO6id6v2nY1o1hTGA3p3uEpuPCZIhRxL2lIr0ITU6FnG d20gKj0X3TAz3OdRCVJRIQEahPRa58B6HvNeP11bGJoSynZnL1hGmak3I5HUZeclOMcz 3PrVAaVIECFn65re4Nrcowry1lMlvL8D5bX82g78LHFOySohsQ6998GkhD772Drh7bxJ 9Hz3/aeBWHntzhHOAeV468ONSSJr0FKARZII3rXg6eosIBg10+edNkh5dI9P9/A9c25R 1dzirrJzJwdbREM6MgGHO9h+B3iTLKzyxJ5LYqDbhC1qvoO6bcHmSC6xHkAMiu3VESvl Qo0g== MIME-Version: 1.0 X-Received: by 10.52.172.68 with SMTP id ba4mr2080462vdc.66.1386367676734; Fri, 06 Dec 2013 14:07:56 -0800 (PST) In-Reply-To: <9df6ccd7-828d-43be-ac49-fe1c6a38bae7@googlegroups.com> References: <9df6ccd7-828d-43be-ac49-fe1c6a38bae7@googlegroups.com> Date: Fri, 6 Dec 2013 17:07:56 -0500 Subject: Re: squeeze out some performance From: Joel Goldstick To: John Ladasky Content-Type: multipart/alternative; boundary=089e0160bc6ee6934504ece4e0a0 Cc: "python-list@python.org" X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 156 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1386368018 news.xs4all.nl 2882 [2001:888:2000:d::a6]:37525 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:61186 --089e0160bc6ee6934504ece4e0a0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, Dec 6, 2013 at 11:52 AM, John Ladasky w= rote: > On Friday, December 6, 2013 12:47:54 AM UTC-8, Robert Voigtl=C3=A4nder wr= ote: > > > I try to squeeze out some performance of the code pasted on the link > below. > > http://pastebin.com/gMnqprST > Not that this will speed up your code but you have this: if not clockwise: s =3D start start =3D end end =3D s Python people would write: end, start =3D start, end You have quite a few if statements that involve multiple comparisons of the same variable. Did you know you can do things like this in python: >>> x =3D 4 >>> 2 < x < 7 True >>> x =3D 55 >>> 2 < x < 7 False > Several comments: > > 1) I find this program to be very difficult to read, largely because > there's a whole LOT of duplicated code. Look at lines 53-80, and lines > 108-287, and lines 294-311. It makes it harder to see what this algorith= m > actually does. Is there a way to refactor some of this code to use some > shared function calls? > > 2) I looked up the "Bresenham algorithm", and found two references which > may be relevant. The original algorithm was one which computed good rast= er > approximations to straight lines. The second algorithm described may be > more pertinent to you, because it draws arcs of circles. > > http://en.wikipedia.org/wiki/Bresenham's_line_algorithm > http://en.wikipedia.org/wiki/Midpoint_circle_algorithm > > Both of these algorithms are old, from the 1960's, and can be implemented > using very simple CPU register operations and minimal memory. Both of th= e > web pages I referenced have extensive example code and pseudocode, and > discuss optimization. If you need speed, is this really a job for Python= ? > > 3) I THINK that I see some code -- those duplicated parts -- which might > benefit from the use of multiprocessing (assuming that you have a > multi-core CPU). But I would have to read more deeply to be sure. I nee= d > to understand the algorithm more completely, and exactly how you have > modified it for your needs. > -- > https://mail.python.org/mailman/listinfo/python-list > --=20 Joel Goldstick http://joelgoldstick.com --089e0160bc6ee6934504ece4e0a0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable



On Fri, Dec 6, 2013 at 11:52 AM, John Ladasky <= ;john_ladas= ky@sbcglobal.net> wrote:
On Frid= ay, December 6, 2013 12:47:54 AM UTC-8, Robert Voigtl=C3=A4nder wrote:

> I try to squeeze out some performance of the code pasted on the link b= elow.
> http://past= ebin.com/gMnqprST

Not that th= is will speed up your code but you have this:

=C2=A0= =C2=A0 if not clockwise:
=C2=A0 =C2=A0 =C2=A0 =C2=A0 s =3D s= tart
=C2=A0 =C2=A0 =C2=A0 =C2=A0 start =3D end
=C2=A0 =C2=A0 =C2=A0 =C2=A0 end =3D s

Python people would w= rite:
=C2=A0=C2=A0=C2=A0 end, start =3D start, end
=C2=A0

You have quite a few if statements that in= volve multiple comparisons of the same variable.=C2=A0 Did you know you can= do things like this in python:

>>> x =3D 4
>>> 2 < x < 7
True
>>= ;> x =3D 55
>>> 2 < x < 7
False
=C2=A0
=
Several comments:

1) I find this program to be very difficult to read, largely because there&= #39;s a whole LOT of duplicated code. =C2=A0Look at lines 53-80, and lines = 108-287, and lines 294-311. =C2=A0It makes it harder to see what this algor= ithm actually does. =C2=A0Is there a way to refactor some of this code to u= se some shared function calls?

2) I looked up the "Bresenham algorithm", and found two reference= s which may be relevant. =C2=A0The original algorithm was one which compute= d good raster approximations to straight lines. =C2=A0The second algorithm = described may be more pertinent to you, because it draws arcs of circles.
=C2=A0 =C2=A0 http://en.wikipedia.org/wiki/Bresenham's_l= ine_algorithm
=C2=A0 =C2=A0 http://en.wikipedia.org/wiki/Midpoint_circle_algori= thm

Both of these algorithms are old, from the 1960's, and can be implement= ed using very simple CPU register operations and minimal memory. =C2=A0Both= of the web pages I referenced have extensive example code and pseudocode, = and discuss optimization. =C2=A0If you need speed, is this really a job for= Python?

3) I THINK that I see some code -- those duplicated parts -- which might be= nefit from the use of multiprocessing (assuming that you have a multi-core = CPU). =C2=A0But I would have to read more deeply to be sure. =C2=A0I need t= o understand the algorithm more completely, and exactly how you have modifi= ed it for your needs.
--
https://mail.python.org/mailman/listinfo/python-list



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