How do I use python object in C++

[lixinyi.23]

for example I have the following code:

#include <Python.h>

void exec_pythoncode( int arg, char**argv )
{
Py_Initialize();
Py_Main(argc,argv);
Py_Finalize();
}

What I would like to know is how can I get the variables I want
after Py_Main(argc,argv)

say I have a=[1,2,'Hello World',0.1234] in the python space,
I would like to have it as a struct in C++.

Any sample code?
Thanks in advance!

 

[Aaron \Castironpi\ Brady]

for example I have the following code:

#include <Python.h>

void exec_pythoncode( int arg, char**argv )
{
    Py_Initialize();
    Py_Main(argc,argv);
    Py_Finalize();

}

What I would like to know is how can I get the variables I want
after Py_Main(argc,argv)

say I have a=[1,2,'Hello World',0.1234] in the python space,
I would like to have it as a struct in C++.

Any sample code?
Thanks in advance!

What do you know about the contents of 'argc' and 'argv'? If it's
impossible with Py_Main, can you use one of the other entry points?

If you've never manipulated PyObject* objects in C, they can be
hairy. Even if you know 'a' is a sequence, its contents are still all
PyObject*s, which you can access via PyList_... and PySequence_
functions.

 

[lixinyi.23]

If the PyObject is a PyList, and all list items are strings,
say a=['aaa','bbb','ccc']

How can I have a
myArray[0] = "aaa"
myArray[1] = "bbb"
myArray[2] = "ccc"
in C++?

Do I have to
use PyModule_GetDict() to get the dict first?
what about the next?

 

[Aaron \Castironpi\ Brady]

If the PyObject is a PyList, and all list items are strings,
say a=['aaa','bbb','ccc']

How can I have a
myArray[0] = "aaa"
myArray[1] = "bbb"
myArray[2] = "ccc"
in C++?

Do I have to
use PyModule_GetDict() to get the dict first?
what about the next?

What do you know about the contents of 'argc' and 'argv'?  If it's
impossible with Py_Main, can you use one of the other entry points?

If you've never manipulated PyObject* objects in C, they can be
hairy.  Even if you know 'a' is a sequence, its contents are still all
PyObject*s, which you can access via PyList_... and PySequence_
functions.

This one writes '[aaa, bbb, ccc]' to the console in two different
ways.

#include <Python.h>

int main() {
PyObject *list, *listrepr;
Py_Initialize();

/* first */
list= PyList_New( 3 );
PyList_SetItem( list, 0, PyString_FromString( "aaa" ) );
PyList_SetItem( list, 1, PyString_FromString( "bbb" ) );
PyList_SetItem( list, 2, PyString_FromString( "ccc" ) );

listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( listrepr );
Py_DECREF( list );

/* second */
list= Py_BuildValue( "[sss]", "aaa", "bbb", "ccc" );
listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( listrepr );
Py_DECREF( list );

Py_Finalize();
return 0;
}

Did you want to execute some Python code, and examine variables it
creates?

 

[Aaron \Castironpi\ Brady]

If the PyObject is a PyList, and all list items are strings,
say a=['aaa','bbb','ccc']

How can I have a
myArray[0] = "aaa"
myArray[1] = "bbb"
myArray[2] = "ccc"
in C++?

Do I have to
use PyModule_GetDict() to get the dict first?
what about the next?

This one writes '[aaa, bbb, ccc]' to the console in two different
ways.

#include <Python.h>

int main() {
    PyObject *list, *listrepr;
    Py_Initialize();

    /* first */
    list= PyList_New( 3 );
    PyList_SetItem( list, 0, PyString_FromString( "aaa" ) );
    PyList_SetItem( list, 1, PyString_FromString( "bbb" ) );
    PyList_SetItem( list, 2, PyString_FromString( "ccc" ) );

    listrepr= PyObject_Repr( list );
    printf( "%s\n", PyString_AsString( listrepr ) );

    Py_DECREF( listrepr );
    Py_DECREF( list );

    /* second */
    list= Py_BuildValue( "[sss]", "aaa", "bbb", "ccc" );
    listrepr= PyObject_Repr( list );
    printf( "%s\n", PyString_AsString( listrepr ) );

    Py_DECREF( listrepr );
    Py_DECREF( list );

    Py_Finalize();
    return 0;

}

Did you want to execute some Python code, and examine variables it
creates?

Here's a third way:

PyObject *list, *listrepr, *dict, *result, *name;
/* third */
dict= PyDict_New( );
result= PyRun_String( "myarray= [ 'ggg', 'hhh', 'iii' ]",
Py_file_input, dict, NULL );
name= PyString_FromString( "myarray" );
list= PyDict_GetItem( dict, name );
listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( dict );
Py_DECREF( result );
Py_DECREF( name );
Py_DECREF( listrepr );
Py_DECREF( list );

PyRun_String runs a namespace, 'dict', which holds the variables.

 

[lixinyi.23]

On Sep 23, 9:30 pm, (e-mail address removed) wrote:

If the PyObject is a PyList, and all list items are strings,
say a=['aaa','bbb','ccc']
How can I have a
myArray[0] = "aaa"
myArray[1] = "bbb"
myArray[2] = "ccc"
in C++?
Do I have to
use PyModule_GetDict() to get the dict first?
what about the next?
What do you know about the contents of 'argc' and 'argv'? If it's
impossible with Py_Main, can you use one of the other entry points?
If you've never manipulated PyObject* objects in C, they can be
hairy. Even if you know 'a' is a sequence, its contents are still all
PyObject*s, which you can access via PyList_... and PySequence_
functions.

This one writes '[aaa, bbb, ccc]' to the console in two different
ways.

#include <Python.h>

int main() {
PyObject *list, *listrepr;
Py_Initialize();

/* first */
list= PyList_New( 3 );
PyList_SetItem( list, 0, PyString_FromString( "aaa" ) );
PyList_SetItem( list, 1, PyString_FromString( "bbb" ) );
PyList_SetItem( list, 2, PyString_FromString( "ccc" ) );

listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( listrepr );
Py_DECREF( list );

/* second */
list= Py_BuildValue( "[sss]", "aaa", "bbb", "ccc" );
listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( listrepr );
Py_DECREF( list );

Py_Finalize();
return 0;

Did you want to execute some Python code, and examine variables it
creates?

Here's a third way:

PyObject *list, *listrepr, *dict, *result, *name;
/* third */
dict= PyDict_New( );
result= PyRun_String( "myarray= [ 'ggg', 'hhh', 'iii' ]",
Py_file_input, dict, NULL );
name= PyString_FromString( "myarray" );
list= PyDict_GetItem( dict, name );
listrepr= PyObject_Repr( list );
printf( "%s\n", PyString_AsString( listrepr ) );

Py_DECREF( dict );
Py_DECREF( result );
Py_DECREF( name );
Py_DECREF( listrepr );
Py_DECREF( list );

PyRun_String runs a namespace, 'dict', which holds the variables.

Thanks! it helps.

I know how to read from python now.

main_module = PyImport_AddModule("__main__");
global_dict = PyModule_GetDict(main_module);
pyObject = PyDict_GetItem(global_dict,key);


it will require lots of type checking, but it's fine to me.