capi-sig July 2010

capi-sig@python.org

8 participants
8 discussions

ANN: expy 0.6.5 released!
by Yingjie Lan 16 Apr '22

16 Apr '22

EXPY is an express way to extend Python! EXPY provides a way to extend python in an elegant way. For more information and a tutorial, see: http://expy.sourceforge.net/ What's new: 1. Correct treatment of __init__ method. 2. Give warnings of missing Py_INCREF on appropriate special type methods. 3. Documentation update. Cheers, Yingjie

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ANNOUNCE: PyBindGen 0.8
by Gustavo Carneiro 10 Mar '22

10 Mar '22

The other day I released PyBindGen 0.8. Main news is that it features a new experimental header file scanner based on pygccxml (i.e., it's similar to py++ in scope, if not in maturity, but does not use boost.pythonunderneath). == What == PyBindGen is a Python module that is geared to generating C/C++ code that binds a C/C++ library for Python. It does so without extensive use of either C++ templates or C pre-processor macros. It has modular handling of C/C++ types, and can be easily extended with Python plugins. The generated code is almost as clean as what a human programmer would write, and does not depend on any library or header files besides Python itself. == Where == https://launchpad.net/pybindgen/ == NEWS == - Support C++ instance attributes through getter/setter methods - Support functions as methods of C++ classes - Support the PyObject* type - Support unsigned int, C strings (char*) (from Mark Lee) - Add basic support for enum types - New experimental automatic module generator based on C/C++ header file scanner and annotations in comments, using pygccxml - Some bug fixes -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert

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C API equivalent to abc.ABCMeta.register?
by Daniel Stutzbach 02 Mar '22

02 Mar '22

I'm the author of an extension module (blist) that provides a type that fits the MutableSequence API. Is there a canonical way for me to register the type as a MutableSequence from the C API? -- Daniel Stutzbach, Ph.D. President, Stutzbach Enterprises, LLC <http://stutzbachenterprises.com>

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Software Development - Application Development - Game Development
by Gary 10 Jan '22

10 Jan '22

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Best practice for new namespace (from C/API)
by Campbell Barton 30 Jul '10

30 Jul '10

Posted to the python developer list but suggested I mail this here instead. --- Hi, I'm writing because I'm working on a project where the user can run scripts that don't reference a file but use internal application text data. Otherwise we are not doing anything tricky, only that the scripts should each run independently (no cruft left from the previous scripts namespace, sharing sys.modules etc is fine). Something which is unclear to me even after looking over pythonrun.c is the correct way to setup a namespace. For years we have been doing this and it seemed to work fine... PyObject *d = PyDict_New(); // new namespace PyDict_SetItemString(d, "__builtins__", PyEval_GetBuiltins()); PyDict_SetItemString(d, "__file__", PyString_FromString(filename)); // fake, avoids sys.argv[0] being used for warnings. /* --- snip ---*/ PyEval_EvalCode(compiled_text, d, d); Recently a developer reported a bug where pickle wasn't working, it turns out that in a few places python expects the __main__ modules namespace to match that if the running script: _pickle.c's save_global() in this case eg: >>> spam = 10 >>> print(__import__("__main__").__dict__["spam"]) ... 10 Once I found this was the problem it was simple to use __main__'s namespace however there are still things that are not clear about exactly how this should be done. Simplified code... PyObject *item, *dict= PyModule_GetDict(PyImport_AddModule("__main__")); PyDict_Clear(dict); PyDict_SetItemString(dict, "__builtins__", PyImport_AddModule("builtins")); item = PyUnicode_FromString( "__main__" ); PyDict_SetItemString( dict, "__name__", item ); Py_DECREF(item); PyDict_SetItemString(d, "__file__", PyString_FromString(filename)); // fake, avoids sys.argv[0] being used for warnings. /* --- snip ---*/ PyEval_EvalCode(compiled_text, dict, dict); Still this leaves me with the following questions... - Whats the best way to manage the namespace for running multiple scripts one after another? clear and initialize __main__'s dict each time?, keep a copy and restore it after each run? - should the original __main__ namespace be restored after running a script? - pickle expects: __import__("__main__").__dict__ == ***the current namespace***, is this apart of the python spec or just something specific to pickle? - PyDict_SetItemString(d, "__builtins__", PyEval_GetBuiltins()) acts differently to PyDict_SetItemString(dict, "__builtins__", PyImport_AddModule("builtins")), using the PyEval_GetBuiltins() dict adds every member of __builtins__ when running: print(__import__("__main__").__dict__.keys()), rather then just showing __builtins__. -- - Campbell

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Threading failure
by Paul Grunau 19 Jul '10

19 Jul '10

I asked this question here a few days ago, and someone suggested I ask again, providing all the code, so that it can be actually tried. So here it is, and I’m still stumped. Original post: I have a problem with threading using the Python/C API. I have an extension that implements a timer, and the C++ timer callback function calls a Python function. The code looks like this: // fetimer.cpp : Defines the exported functions for timer function. #define_WIN32_WINNT 0x502 #include"stdafx.h" #include"mmsystem.h" #include"python.h" #defineTARGET_RESOLUTION 1 UINT wTimerRes,fooval; BOOL LEDflag,timeFlag; BOOL timerActive = FALSE; BOOL timerSet = FALSE; BOOL funcsetFlag = FALSE; BOOL modsetFlag = FALSE; BOOL attrsetFlag = FALSE; UINT wTimerID,timeval,setVal = 2000; HANDLE porthandle; TIMECAPS tc; UINT userval,*pVal; PyObject *mod, *attr, *pargs, *pres; UINT SetTimerCallback( UINT wTimrID, UINT msInterval ); staticvoid CALLBACK PeriodicTimer(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2); PyObject *ProcessTimer( void ); PyObject *pymod; PyObject *pattr; PyObject *foop; staticvoid (*pFunc)(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2); staticPyObject *timer_setup( PyObject *pSelf, PyObject *pArgs ) { if (timeGetDevCaps(&tc, sizeof(TIMECAPS)) != TIMERR_NOERROR) { } wTimerRes = min(max(tc.wPeriodMin, TARGET_RESOLUTION), tc.wPeriodMax); timeBeginPeriod(wTimerRes); LEDflag = FALSE; timeFlag = FALSE; timerActive = FALSE; userval = 123; pVal = &userval; Py_Initialize(); fooval = 0; return Py_None; } staticPyObject *timer_start( PyObject *pSelf, PyObject *pArgs ) { int tval = 2000; if( timerActive ){ timeKillEvent( wTimerID ); } if( timerSet ){ tval = setVal; } UINT retval = SetTimerCallback( wTimerID, tval ); timerActive = TRUE; return Py_None; } UINT SetTimerCallback(UINT wTimrID, // sequencer data UINT msInterval) // event interval { wTimerID = timeSetEvent( msInterval, // delay wTimerRes, // resolution (global variable) (LPTIMECALLBACK)PeriodicTimer, // callback function wTimrID, // user data TIME_PERIODIC|TIME_CALLBACK_FUNCTION ); if(!wTimerID) { return 999; } else{ return 0; } } staticvoid CALLBACK PeriodicTimer(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2) { PyGILState_STATE pgs; pgs = PyGILState_Ensure(); if(attrsetFlag) { pres = PyObject_CallFunction(attr,NULL); if( pres == NULL )printf("CallFunction failed!\n"); } PyGILState_Release( pgs ); } staticPyObject *timer_kill( PyObject *pSelf, PyObject *pArgs ) { timeKillEvent( wTimerID ); timerSet = FALSE; timerActive = FALSE; return Py_None; } staticPyObject *timer_settime( PyObject *pSelf, PyObject *pArgs ) { UINT t; PyArg_ParseTuple( pArgs, "i", &t ); setVal = t; timerSet = TRUE; return Py_None; } staticPyObject *timer_setmodname( PyObject *pSelf, PyObject *pArgs ) { char *b; PyArg_ParseTuple( pArgs, "s", &b ); mod = PyImport_ImportModule(b); if( mod == NULL ) { printf("Could not import %s\n",b); return Py_None; } modsetFlag = TRUE; return Py_None; } staticPyObject *timer_setprocname( PyObject *pSelf, PyObject *pArgs ) { char *b; if( !modsetFlag )return Py_None; PyArg_ParseTuple( pArgs, "s", &b ); attr = PyObject_GetAttrString(mod,b); if( attr == NULL ) { printf("Could not import %s\n",b); return Py_None; } attrsetFlag = TRUE; return Py_None; } staticPyMethodDef fetimer_methods[] = { {"timer", timer_setup, METH_VARARGS, "blah"}, {"start", timer_start, METH_VARARGS, "start timer" }, {"kill", timer_kill, METH_VARARGS, "kill timer" }, {"settime", timer_settime, METH_VARARGS, "set timer" }, {"setmodname", timer_setmodname, METH_VARARGS, "set module name" }, {"setprocname", timer_setprocname, METH_VARARGS, "set procedure name" }, {NULL, NULL} }; PyMODINIT_FUNC initfetimer(void) { Py_InitModule("fetimer", fetimer_methods); } The Python code (Timetest3.py) that sets this up looks like this: #Time Test 3.py import fetimer #import feserial import time Hit = 0 L = 0 fetimer.timer() fetimer.settime(30) fetimer.setmodname("Timeslice3") fetimer.setprocname("Timetester") #feserial.open(4) #feserial.dtr(0) print "\n Program Waiting for Time Slice" fetimer.start() while True: time.sleep(0.010) and the module Timeslice3.py looks like this: #Timeslice3.py def Timetester(): pass The application should run by entering "python timetest3.py" at the command prompt. When I run this stuff, it works fine for hundreds, often even thousands, of timer ticks (I’ve been testing with about thirty ticks per second, but it doesn’t matter – it still crashes at ten or fewer ticks per second). Sometimes it runs for only a few seconds, sometimes for ten minutes or so. But it always eventually crashes Python. Usually it gives no error message. Sometimes, though, it does give an error message, but not always the same one. I’ve noted three that it has given in my testing so far: Fatal Python Error: This thread state must be current when releasing Fatal Python Error: PyThreadState_DeleteCurrent: no current tstate Fatal Python Error: PyEval_SaveThread: NULL tstate Can anybody help me make this code stable, so that it works all the time? I’m using Python 2.6.5 under Windows Vista, but it crashes under Windows XP as well.

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DECREF when using PyDict_SetItem...
by Tim Golden 02 Jul '10

02 Jul '10

I'm using PyDict_SetItemString to add a long from a C struct into a Python dictionary. The full code is in the usn2dict function in here: http://svn.timgolden.me.uk/extensions/change-journal/_usn.c but the sort of thing I'm talking about is this: PyDict_SetItemString ( dict, "RecordLength", PyLong_FromLongLong (usn_record->RecordLength) ); My understanding is that PyLong_FromLongLong passes its reference to my function, which then passes it to PyDict_Set... which INCREFs it. That means, I think, that my function should DECREF it before exit since I'm only creating it to store it in the dict. Is that correct? In other words, should my code really do this? record_length = PyLong_FromLongLong (usn_record->RecordLength); PyDict_SetItemString (dict, "RecordLength", record_length); Py_DECREF (record_length) Thanks TJG

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intermittent failure of threading
by Paul Grunau 02 Jul '10

02 Jul '10

I have a problem with threading using the Python/C API. I have an extension that implements a timer, and the C++ timer callback function calls a Python function. The relevant code looks like this: staticPyObject *timer_setmodname( PyObject *pSelf, PyObject *pArgs ) { char *b; PyArg_ParseTuple( pArgs, "s", &b ); mod = PyImport_ImportModule(b); if( mod == NULL ) { printf("Could not import %s\n",b); return Py_None; } modsetFlag = TRUE; return Py_None; } staticPyObject *timer_setprocname( PyObject *pSelf, PyObject *pArgs ) { char *b; if( !modsetFlag )return Py_None; PyArg_ParseTuple( pArgs, "s", &b ); attr = PyObject_GetAttrString(mod,b); if( attr == NULL ) { printf("Could not import %s\n",b); return Py_None; } attrsetFlag = TRUE; return Py_None; } staticvoid CALLBACK PeriodicTimer(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2) { PyGILState_STATE pgs; pgs = PyGILState_Ensure(); if(attrsetFlag) { pres = PyObject_CallFunction(attr,NULL); if( pres == NULL )printf("CallFunction failed!\n"); } PyGILState_Release( pgs ); } The Python code that sets this up looks like this: fetimer.setmodname("Timeslice3") fetimer.setprocname("Timetester") print "\n Program Waiting for Time Slice" while True: time.sleep(0.010) and the module Timeslice3.py looks like this: #Timeslice3.py def Timetester(): pass When I run this stuff, it works fine for hundreds, often even thousands, of timer ticks (I’ve been testing with about thirty ticks per second, but it doesn’t matter – it still crashes at ten or fewer ticks per second). Sometimes it runs for only a few seconds, sometimes for ten minutes or so. But it always eventually crashes Python. Usually it gives no error message. Sometimes, though, it does give an error message, but not always the same one. I’ve noted three that it has given in my testing so far: Fatal Python Error: This thread state must be current when releasing Fatal Python Error: PyThreadState_DeleteCurrent: no current tstate Fatal Python Error: PyEval_SaveThread: NULL tstate Can anybody help me make this code stable, so that it works all the time? I’m using Python 2.6.5 under Windows Vista, but it crashes under Windows XP as well.

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capi-sig July 2010