capi-sig January 2009

capi-sig@python.org

12 participants
7 discussions

by Gamze Tunali

Hi, As a beginner, I have a question about passing a class instance from Python script to my C code. What I am doing is basically creating a class in the script: class dbvalue: def __init__(self, index, type): self.id = index # unsigned integer self.type = type # string last_roi = dbvalue(id, type); bmdl_batch.set_input_from_db(1, last_roi); <-------- I would like to call my C function with last_roi and able to recover id and type in the code. The C part is follows: PyObject *set_input_from_db(PyObject* self, PyObject *args) { unsigned input; PyObject *obj; if (!PyArg_ParseArg(args, "iO:set_input_from_db", &input, &obj)) return NULL; .... } I am not sure if PyArg_ParseArg() is the right method to get the object. I used "O:.." to get it but after that, how do I acces index and type fields of the object. Do I create an equivalent class/struct in C code to? Again, all I want is pass the 2 values together in an object and able to recover then in C code. Thanks, Gamze

11 years, 4 months

Strange Python behaviour after C-Function

by Philipp Heuser

Hi all, thanks for the numerous replies to my previous questions. Everything in C works fine so far, but there is a very strange behaviour in python after visiting the C-Function. The return value of my C-Function is a list of floats. I can print that list, I can do: a=0 while a<len(list): print list[a] a=a+1 works fine, but if try to do for element in list: print element It does that as well, but as soon as the end of the list is reached, I do get an IndexError: list assignment index is out of range. Surprisingly I do get that as well with any list, where I try to use the for loop after using the C-function. So if I use an arbitrary list like ll=[1,2,3] for l in ll: print l I do get the same error, and I don't before calling the C-function... Does that sound familiar to anybody? Is that caused by one of the decref/incref things? Kind regards Philipp

11 years, 4 months

Some problem when i use Python C/API to embed python script, need Help......

by zouxianjun 45728

when the program run as exe, everything goes right, but if i compile the program as a .so lib, use other program to load the .so lib and run, it goes wrong,in the lib i also use PyRun_SimpleString("import base64"); it goes wrong.....my python version is 2.3, i want to know what's the problem...... PyErr_Print() print the error info below: Traceback (most recent call last): File "./myModule111.py", line 3, in ? import base64 File "/usr/lib/python2.3/base64.py", line 7, in ? import binascii ImportError: /usr/lib/python2.3/lib-dynload/binascii.so: undefined symbol: PyExc_TypeError i check the binascii.so, ldd -r binascii.so, this lib really has many undefined symbols include PyExc_TypeError, but the problem is when the program is executable, it can goes fine...... when i compile the program as .so lib, i add -Xlinker -export-dynamic, it doesn't solve the problem......... ****************************************************************************************** This email and its attachments contain confidential information from HUAWEI, which is intended only for the person or entity whose address is listed above. Any use of the information contained here in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this email in error, please notify the sender by phone or email immediately and delete it! *****************************************************************************************

11 years, 4 months

How to manipulate C table as python list ?

by Marc

Hi, I would like to use a C program which manipulates table as a python module acting on a list. My C code is the following: int sum(int *tab, int n) { int i, s = 0; for (i=0; i<n; i++) { s += tab[i]; } return s; } Now, I would like to use it as a python module where tab would be a python list. I read some examples in the documentation but the size of the list is always assumed to be known such that one can use PyArg_ParseTuple with a format description for each argument. I would like that my module behave like: a=[1,2,3] b=[2,8,20] print my_module.sum(a) -> 6 print my_module.sum(b) -> 30 My question is: which option should I use with PyArg_ParseTuple? I'm totaly lost with all its option (O, O&, O!, etc) Thx, Marc.

11 years, 4 months

Py_BuildValue, Array from C to Python

by Philipp Heuser

Hi all, I am trying to return an array from C to Python. Since it is of variable size, return Py_BuildValue("[f,f,f]", array[0], array[1], array[2]); does not help. How do I do that? Any help is appreciated, kind regards Philipp

11 years, 4 months

Compiling for multiple versions of libpython2

by Patrick Moore

Hi all, Currently we have a python/c hybrid which works well and compiles against 2.3 and up nicely, and runs sensibly against all of these, however we still need to compile directly against the correct python library before distribution. The question is, do any of you know a sensible way of compiling and opening the python libraries such that, so long as the end user has at least python2.3 libs (and compatible apis), that it will automagically just run. This is primarily to avoid end users having multiple versions of python on there systems, and to aid us with only having to build and test one exectuable. All suggestions greatly welcomed as we're struggling to find an elegant solution to this. cheers, paddy -- ----------( I am an idiot )---------- paddy ----( )---- yddap Htag.pl 0.0.23

11 years, 4 months

Getting full traceback text

by Campbell Barton

recently I have been experimenting with a new api for blender3d, one of the things it needs to be able to do is give python errors (tracebacks) to our own error reporting api. The problem is that Python/C api has no way to get the text that PyErr_Print() prints, as a string. This seems not such an unusual thing for an api to require, after all, many applications dont run with a console to display text. So far I think there are 3 ways to do this. * Create a pipe, open it with fdopen(), then temporarily replace stderr and stdout and call PyErr_Print().... then get the text from that pipe. I havnt tried this yet and I'm not sure if its a good cross platform solution. * Copy and paste Pythons C traceback function into my own function that builds a string rather then printing it. This really isnt an attractive option. * Use pythons traceback module from C (this isnt so bad, but Id prefer not to have core parts of our api relying on *.py modules) Is there some other way to do this? or is anyone currently doing this in their application? Here is the Python 3.x C api code for getting the traceback. -------------------- snip static void pyop_error_report(ReportList *reports) { /* # in python this would be... import traceback string = ' '.join(traceback.format_exc()) */ PyObject *type, *value, *traceback; PyObject *mod; PyObject *ret, *list, *string, *args; /* Save the current exception */ PyErr_Fetch(&type, &value, &traceback); mod = PyImport_ImportModule("traceback"); if (!mod) { /* print some error */ return; } list= PyObject_CallMethod(mod, "format_exception", "OOO", type, value, traceback); string= PyUnicode_FromString("\n"); ret= PyUnicode_Join(string, list); Py_DECREF(list); Py_DECREF(string); BKE_report(reports, RPT_ERROR, _PyUnicode_AsString(ret)); Py_DECREF(ret); PyErr_Clear(); } -------------------- -- - Campbell

11 years, 4 months

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capi-sig January 2009