Re: ctypes question
On Dec 11, 12:59 pm, MrJean1 mrje...@gmail.com wrote: In general, for shared libraries, you need to define those first as prototype using ctypes.CFUNCTYPE() and then instantiate each prototype once supplying the necessary parameter flags using prototype(func_spec, tuple_of_param_flags). See sections 15.16.2.3 and 4 of the ctypes docs*. I tried the cfuntype and proto steps, and it's not crashing now (that's good), but now i'm just left with null pointers as a return object. I'm still working through all of the examples you sent. They were extremely helpful. Here's where I'm at now... What is strange is I can actually get smiGetNode to work if I don't cfunctype/proto it. If i do, nada. however, the smiGetNextNode fails no matter what, usually with a segfault, but depending on how i construct it, sometimes a null pointer. constants.py: http://pastebin.com/f3b4Wbf0 libsmi.py: http://pastebin.com/XgtpG6gr smi.c (the actual function): http://pastebin.com/Pu2vabWM -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
Try again after changing line 16 to sn = SmiGetNode(None, 1.3.6.1.2.1.2.2) Because, SmiGetNode is a Python function which accepts Python objects as arguments. Passing is a ctypes object oid is incorrect. /Jean On Dec 14, 10:36 am, News Wombat newswom...@gmail.com wrote: On Dec 11, 12:59 pm, MrJean1 mrje...@gmail.com wrote: In general, for shared libraries, you need to define those first as prototype using ctypes.CFUNCTYPE() and then instantiate each prototype once supplying the necessary parameter flags using prototype(func_spec, tuple_of_param_flags). See sections 15.16.2.3 and 4 of the ctypes docs*. I tried the cfuntype and proto steps, and it's not crashing now (that's good), but now i'm just left with null pointers as a return object. I'm still working through all of the examples you sent. They were extremely helpful. Here's where I'm at now... What is strange is I can actually get smiGetNode to work if I don't cfunctype/proto it. If i do, nada. however, the smiGetNextNode fails no matter what, usually with a segfault, but depending on how i construct it, sometimes a null pointer. constants.py:http://pastebin.com/f3b4Wbf0 libsmi.py:http://pastebin.com/XgtpG6gr smi.c (the actual function):http://pastebin.com/Pu2vabWM -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
News Wombat newswom...@gmail.com wrote in message news:413f5a8f-69a0-4351-acc2-18d7edda8...@j3g2000vbp.googlegroups.com... On Dec 11, 12:59 pm, MrJean1 mrje...@gmail.com wrote: In general, for shared libraries, you need to define those first as prototype using ctypes.CFUNCTYPE() and then instantiate each prototype once supplying the necessary parameter flags using prototype(func_spec, tuple_of_param_flags). See sections 15.16.2.3 and 4 of the ctypes docs*. I tried the cfuntype and proto steps, and it's not crashing now (that's good), but now i'm just left with null pointers as a return object. I'm still working through all of the examples you sent. They were extremely helpful. Here's where I'm at now... What is strange is I can actually get smiGetNode to work if I don't cfunctype/proto it. If i do, nada. however, the smiGetNextNode fails no matter what, usually with a segfault, but depending on how i construct it, sometimes a null pointer. constants.py: http://pastebin.com/f3b4Wbf0 libsmi.py: http://pastebin.com/XgtpG6gr smi.c (the actual function): http://pastebin.com/Pu2vabWM -- http://mail.python.org/mailman/listinfo/python-list constants.py, in SmiNode and SmiModule definitions: - Any field defined char* in C should be c_char_p not POINTER(c_char_p) (which is char**). The function definition can be simplified, and 2nd argument corrected (c_char_p not POINTER(c_char_p)). Python strings can be passed directly to c_char_p arguments. SmiGetNode = clibsmi.smiGetNode SmiGetNode.argtypes = [POINTER(SmiModule),c_char_p] SmiGetNode.restype = POINTER(SmiNode) oid = 1.3.6.1.2.1.2.2 sn=SmiGetNode(None,oid) Give these fixes a try... -Mark -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
It is not entirely clear what the functions and especially what their signatures are in that C library clibsmi. In general, for shared libraries, you need to define those first as prototype using ctypes.CFUNCTYPE() and then instantiate each prototype once supplying the necessary parameter flags using prototype(func_spec, tuple_of_param_flags). See sections 15.16.2.3 and 4 of the ctypes docs*. Take a look the Python bindings** for the VLC library, the file called vlc.py***. The function _Cfunction is used to create the Python callable for each C function in that VLC library. All the Python callables are in the second half of the vlc.py file, starting at line 2600. Hope this helps, /Jean *) http://docs.python.org/library/ctypes.html#foreign-functions **) http://wiki.videolan.org/Python_bindings ***) http://git.videolan.org/?p=vlc/bindings/ python.git;a=tree;f=generated;b=HEAD On Dec 10, 3:32 pm, News Wombat newswom...@gmail.com wrote: Hi everyone, I've been experimenting with the ctypes module and think it's great. I'm hitting a few snags though with seg faults. I attached two links that holds the code. The line i'm having problems with is this, sn=clibsmi.smiGetNextNode(pointer(sno),SMI_NODEKIND_ANY) It will work one time, and if I call it again with the result of the previous, even though the result (a c struct) looks ok, it will segfault. I think it's a problem with pointers or maybe the function in the c library trying to change a string that python won't let it change. I'm stuck, any tips would be appreciated. Thanks, and Merry Christmas! constants.py:http://pastebin.com/HvngjzZN libsmi.py:http://pastebin.com/19C9kYEa -- http://mail.python.org/mailman/listinfo/python-list
ctypes question
Hi everyone, I've been experimenting with the ctypes module and think it's great. I'm hitting a few snags though with seg faults. I attached two links that holds the code. The line i'm having problems with is this, sn=clibsmi.smiGetNextNode(pointer(sno),SMI_NODEKIND_ANY) It will work one time, and if I call it again with the result of the previous, even though the result (a c struct) looks ok, it will segfault. I think it's a problem with pointers or maybe the function in the c library trying to change a string that python won't let it change. I'm stuck, any tips would be appreciated. Thanks, and Merry Christmas! constants.py: http://pastebin.com/HvngjzZN libsmi.py: http://pastebin.com/19C9kYEa -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
News Wombat newswom...@gmail.com wrote in message news:2abdd9b3-66ec-4125-a5f8-41315008c...@l17g2000yqe.googlegroups.com... Hi everyone, I've been experimenting with the ctypes module and think it's great. I'm hitting a few snags though with seg faults. I attached two links that holds the code. The line i'm having problems with is this, sn=clibsmi.smiGetNextNode(pointer(sno),SMI_NODEKIND_ANY) It will work one time, and if I call it again with the result of the previous, even though the result (a c struct) looks ok, it will segfault. I think it's a problem with pointers or maybe the function in the c library trying to change a string that python won't let it change. I'm stuck, any tips would be appreciated. Thanks, and Merry Christmas! constants.py: http://pastebin.com/HvngjzZN libsmi.py: http://pastebin.com/19C9kYEa Well, I can't run your code, but I think you should pass the original sn pointer from smiGetNode() and not a pointer(sno). The values are not the same and the library probably relies on passing the original pointer back into smiGetNextNode. sn.contents returns a new SmiNode object so its pointer will be different. -Mark -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
On Wed, Apr 14, 2010 at 12:12 PM, Mark Dickinson dicki...@gmail.com wrote: On Apr 14, 7:09 pm, Brendan Miller catph...@catphive.net wrote: I'm using python 2.5.2. I have a ctypes function with argtypes like this: _create_folder.argyptes = [c_void_p, c_int] Is that line a cut-and-paste? If so, try 'argtypes' instead of 'argyptes'. :) Woops! Well, nice to know that ctypes works as I expect. -- http://mail.python.org/mailman/listinfo/python-list
ctypes question
I'm using python 2.5.2. I have a ctypes function with argtypes like this: _create_folder.argyptes = [c_void_p, c_int] The issue I am having is that I can call it like this _create_folder(some_pointer, asdf) and it won't raise a TypeError. Why would it accept a string for an integer argument? I didn't see this behavior documented when I read through http://docs.python.org/library/ctypes.html, maybe I'm just missing it... if that's the case a reference would be appreciated. Brendan -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question
On Apr 14, 7:09 pm, Brendan Miller catph...@catphive.net wrote: I'm using python 2.5.2. I have a ctypes function with argtypes like this: _create_folder.argyptes = [c_void_p, c_int] Is that line a cut-and-paste? If so, try 'argtypes' instead of 'argyptes'. :) The issue I am having is that I can call it like this _create_folder(some_pointer, asdf) and it won't raise a TypeError. Why would it accept a string for an integer argument? I get the expected TypeError in 2.5.4 (OS X) (using printf, for lack of anything better): Python 2.5.4 (r254:67916, Feb 11 2010, 00:50:55) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type help, copyright, credits or license for more information. from ctypes import * libc = CDLL(libc.dylib) libc CDLL 'libc.dylib', handle 8fe46768 at 1a2330 printf = libc.printf printf.argtypes = [c_char_p, c_int] printf(%d\n, 53) 53 3 printf(%d\n, asdf) Traceback (most recent call last): File stdin, line 1, in module ctypes.ArgumentError: argument 2: type 'exceptions.TypeError': wrong type -- Mark -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question about call by reference
At Sunday 24/9/2006 15:49, Lawrence Oluyede wrote: Is it at all possbile to use a struct without defining it with ctypes? If you want to use it you have to define it somewhere... If it's an opaque thing, totally managed by the external code, yes - treat it as a pointer. That is, if you never have to access its fields, or create/destroy it in the python code (using an external function would be ok). Gabriel Genellina Softlab SRL __ Preguntá. Respondé. Descubrí. Todo lo que querías saber, y lo que ni imaginabas, está en Yahoo! Respuestas (Beta). ¡Probalo ya! http://www.yahoo.com.ar/respuestas -- http://mail.python.org/mailman/listinfo/python-list
ctypes question about call by reference
Hi, hopefully someone with some ctypes experience can help me. I guess this is a trivial task again, but I have been googling, reading, experimenting the whole afternoon without any success. I have a given C function signature: char *MagickGetException(MagickWand *wand,ExceptionType *severity) - ExceptionType is an enum - MagickWand is somewhat strange, but so far it works fine without any type mangling. How would I wrap this thing using ctypes? Can anybody help me with that? Best regards, Oliver -- Oliver Andrich [EMAIL PROTECTED] --- http://roughbook.de/ -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question about call by reference
Oliver Andrich [EMAIL PROTECTED] wrote: - ExceptionType is an enum - MagickWand is somewhat strange, but so far it works fine without any type mangling. How would I wrap this thing using ctypes? Can anybody help me with that? First thing first: you have to identify how ExceptionType and MagickWand are composed of. Then you can start wrapping them following the instructions in the tutorial: http://docs.python.org/lib/ctypes-ctypes-tutorial.html -- Lawrence - http://www.oluyede.org/blog Nothing is more dangerous than an idea if it's the only one you have - E. A. Chartier -- http://mail.python.org/mailman/listinfo/python-list
Re: Re: ctypes question about call by reference
On 9/24/06, Lawrence Oluyede [EMAIL PROTECTED] wrote: Oliver Andrich [EMAIL PROTECTED] wrote: - ExceptionType is an enum - MagickWand is somewhat strange, but so far it works fine without any type mangling. How would I wrap this thing using ctypes? Can anybody help me with that? First thing first: you have to identify how ExceptionType and MagickWand are composed of. Then you can start wrapping them following the instructions in the tutorial: http://docs.python.org/lib/ctypes-ctypes-tutorial.html Well, what I learned so far from the documentation, which I already have read more then once today, is that there is no example for an enum in this situation. But looking at pygame-sdl and another project, it looks like the enum is just an c_int or c_long. And concerning MagickWand, I think I have learned, that I don't need to define the structure, if I don't want to access it. And I don't want to, cause this is handled by the library itself. Another point in this context is also, that it is not defined in the header files distributed with the library, but only in the source from which the library is built. As the file is named magick-wand-private.h it is also not meant to be edited. Is it at all possbile to use a struct without defining it with ctypes? Is it okay, to just use the int which is returned by default? Most of my library works with that configuration, so I thought it is working. Based on this, can you give me some more hints? Best regards, Oliver -- Oliver Andrich [EMAIL PROTECTED] --- http://roughbook.de/ -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes question about call by reference
Oliver Andrich [EMAIL PROTECTED] wrote: Well, what I learned so far from the documentation, which I already have read more then once today, is that there is no example for an enum in this situation. But looking at pygame-sdl and another project, it looks like the enum is just an c_int or c_long. The documentation explains how to build an enum to pass to a function: http://docs.python.org/lib/ctypes-structures-unions.html See the first sentence. class ExceptionType(Union): _fields_ = [list_of_tuples] Is it at all possbile to use a struct without defining it with ctypes? If you want to use it you have to define it somewhere... Is it okay, to just use the int which is returned by default? Most of my library works with that configuration, so I thought it is working. I see your functions returns a char * so I don't understand what are you saying here... Based on this, can you give me some more hints? It's not really clear :-) -- Lawrence - http://www.oluyede.org/blog Nothing is more dangerous than an idea if it's the only one you have - E. A. Chartier -- http://mail.python.org/mailman/listinfo/python-list
Re: Re: ctypes question about call by reference
After a walk outside, some fresh air around my nose and some time to relax, I finally found out how to do, what I want to do. First, define the argument types and the result type. _dll.MagickGetException.argtypes = (c_long, POINTER(c_long)) _dll.MagickGetException.restype = c_char_p Second, write correct code as it is documented. :) def get_magick_exception(wand): severity = c_long() description = _dll.MagickGetException(wand, byref(severity)) return (severity, description) And thats all. I just did the call to POINTER(c_long) in the wrong location. Now I do it as documented, and I get everything I want. I can btw live perfectly without definining what actually a MagickWand is, cause from the point of the developer just using the library and documentation, he doesn't know about the actual structure of it. The definition is hidden the C source of the library, and is not documented in the public interface. Thanks and Regards, Oliver. -- Oliver Andrich [EMAIL PROTECTED] --- http://roughbook.de/ -- http://mail.python.org/mailman/listinfo/python-list
