DseWiki: MarkusRechberger/Python

Writing C extensions using direct python api

Alle variablen die intern in einer funktion benutzt werden müssen sofern sie nicht ins python zurückgeliefert werden wieder gelöscht werden. dies geschieht mittels PyObject? -> {Py DECREF}?(variable);

main.c
#include <Python.h> static PyObject * main_system(PyObject *self, PyObject *args) { char *command; if(!PyArg_ParseTuple(args,"s",&command)) return NULL; fprintf(stderr,"%s\n",command); return Py_BuildValue("s","executed!"); } static PyMethodDef MainMethods[]={ {"system",main_system,METH_VARARGS,"Execute method."}, {NULL,NULL,0,NULL} }; PyMODINIT_FUNC initmain(void) { PyObject *m; m=Py_InitModule("main",MainMethods); }

setup.py:
from distutils.core import setup,Extension module1 = Extension('main', sources=['main.c']) #from distutils import sysconfig #save_init_posix = sysconfig._init_posix #def my_init_posix(): # print 'my_init_posix: changing gcc to g++' # save_init_posix() # g = sysconfig._config_vars # g['CC'] = 'g++' # g['LDSHARED'] = 'g++ -shared' #sysconfig._init_posix = my_init_posix setup (name = 'main', version = '1.0', description = 'Demopackage', ext_modules = [module1])

Makefile:
all: # env CXX=g++ python setup.py build python setup.py build clean: python setup.py clean install: python setup.py install

building

make

Running

# python Python 2.3.3 (#2, Jan 13 2004, 00:47:05) [GCC 3.3.3 20040110 (prerelease) (Debian)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import main >>> print main.system("foo") foo executed! >>> d=main.system("foo") foo >>> print d executed! >>>

Writing python modules using swig C++

sample.h
#include <string> std::string returnstring(){ return std::string("string"); }

sample.i
%{ #include "sample.h" %} #include "sample.h"

Makefile
TOP = ../.. SWIG = swig-1.3 CXXSRCS = TARGET = sample INTERFACE = sample.i LIBS = -lm SWIG = swig-1.3 all:: $(MAKE) -f $(TOP)/Makefile CXXSRCS='$(CXXSRCS)' SWIG='$(SWIG)' SWIGOPT='$(SWIGOPT)' TARGET='$(TARGET)' INTERFACE='$(INTERFACE)' python_cpp static:: $(MAKE) -f $(TOP)/Makefile CXXSRCS='$(CXXSRCS)' SWIG='$(SWIG)' SWIGOPT='$(SWIGOPT)' TARGET='mypython' INTERFACE='$(INTERFACE)' python_cpp_static clean:: $(MAKE) -f $(TOP)/Makefile python_clean rm -f $(TARGET).py check: all

see swig1.3 sample directory in debian but sample.h is almost all you need

Writing python modules using swig and C

For using swig with C, you always need a Interface file (with the same name, only with i as extension)

the c File

sample.c

#include <string.h>
#include "userLibrary.h"

void somefunction(){
   ... do something here ...
}

the interface file for swig

sample.i

%module sample
%{
/* Put header files here (optional) */
#include "userLibrary.h"
%}
%include "userLibrary.h"

extern void somefunction();

make and compile and create the python library

> swig -python sample.i

> gcc -c sample.c sample_wrap.c -I/usr/include/python2.3

> ld -shared sample.o sample_wrap.o -o _sample.so -L(librarys)

at last in python

python

>>> import sample

>>> sample.somefunction()

python memory management

http://evanjones.ca/python-memory.html