Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'sys': 0.05; 'attributes': 0.07; 'incompatible': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:ctypes': 0.09; 'tuple': 0.09; 'typeerror:': 0.09; 'python': 0.11; 'skip:f 30': 0.15; 'array)': 0.16; 'brilliant': 0.16; 'peek': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:plane.gmane.org': 0.16; 'received:t-ipconnect.de': 0.16; 'structure.': 0.16; 'wrote:': 0.16; 'documented': 0.18; '>>>': 0.20; '(or': 0.21; '"",': 0.22; 'ctypes': 0.22; 'code.': 0.23; 'passing': 0.23; 'slightly': 0.23; "i've": 0.24; 'import': 0.24; '(most': 0.24; 'header:User-Agent:1': 0.26; 'header:X-Complaints- To:1': 0.26; 'required.': 0.26; 'least': 0.27; "doesn't": 0.28; 'actual': 0.29; "i'm": 0.29; 'arrays': 0.29; 'cat': 0.29; 'yields': 0.29; '-----': 0.29; 'array': 0.29; 'becomes': 0.31; 'print': 0.31; 'source': 0.31; 'structure': 0.32; 'class': 0.33; 'traceback': 0.33; 'file': 0.34; 'skip:c 30': 0.35; 'to:addr :python-list': 0.35; 'instance': 0.35; 'but': 0.36; 'subject:: ': 0.37; 'instead': 0.38; 'received:org': 0.38; 'to:addr:python.org': 0.39; 'data': 0.40; 'received:de': 0.40; 'further': 0.60; 'more': 0.62; 'mar': 0.65; 'results': 0.66; 'reflection': 0.84; '2014,': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: ctypes and byte order Date: Thu, 18 Jun 2015 14:24:03 +0200 Organization: None References: <678134472.4779269.1434626735692.JavaMail.root@sequans.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p57bd8c90.dip0.t-ipconnect.de User-Agent: KNode/4.13.3 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ 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: 61 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1434630262 news.xs4all.nl 2908 [2001:888:2000:d::a6]:53750 X-Complaints-To: abuse@xs4all.nl Path: csiph.com!usenet.pasdenom.info!news.stben.net!border1.nntp.ams1.giganews.com!nntp.giganews.com!newsfeed.xs4all.nl!newsfeed8.news.xs4all.nl!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Xref: csiph.com comp.lang.python:92825 Jean-Michel Pichavant wrote: > ----- Original Message ----- >> From: "Peter Otten" <__peter__@web.de> >> becomes >> >> $ cat be2.py >> import ctypes, sys >> >> iarray_be = ctypes.c_uint32.__ctype_be__*5 >> >> class Foo_be(ctypes.BigEndianStructure): >> _fields_ = [('bar', iarray_be)] >> >> print sys.version >> f_be = Foo_be((0,1,2,3,0x11223344)) >> print hex(f_be.bar[4]) >> >> $ python be2.py >> 2.7.6 (default, Mar 22 2014, 22:59:56) >> [GCC 4.8.2] >> 0x11223344L >> >> which might do what you want. > > Brilliant ! > > I've tested it and it yields the exact same results (binary file content > wise) than my "workaround" structure. But that's way better since my > actual structure is more complex and arrays will be required. > > Though I'm slightly puzzled by the ctypes author(s) choice, this is not > documented and requires to peek into the source code. Dunder attributes > are rarely part of an interface. On further reflection it dawned on me that what may have made this work is passing in the tuple instead of an array: >>> import ctypes >>> array = ctypes.c_uint32 * 3 >>> class B(ctypes.BigEndianStructure): ... _fields_ = [("bar", array)] ... >>> b = B((1,2,3)) >>> b.bar >>> b.bar[2] 3L >>> b = B(array(1,2,3)) Traceback (most recent call last): File "", line 1, in TypeError: incompatible types, c_uint_Array_3 instance instead of c_uint_be_Array_3 instance Oops... So the only thing that doesn't work transparently is initialising a data structure (or at least array) from its "other-endian" twin.