How do I use python object in C++

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  • lixinyi.23@gmail.com
    #1

    How do I use python object in C++

    for example I have the following code:

    #include <Python.h>

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

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

    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!
    Tags: None
    • Aaron \Castironpi\ Brady
      #2
      Re: How do I use python object in C++

      On Sep 23, 7:50 pm, lixinyi...@gmai l.com wrote:
      for example I have the following code:
      >
      #include <Python.h>
      >
      void exec_pythoncode ( int arg, char**argv )
      {
          Py_Initialize() ;
          Py_Main(argc,ar gv);
          Py_Finalize();
      >
      }
      >
      What I would like to know is how can I get the variables I want
      after Py_Main(argc,ar gv)
      >
      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.

        Comment

        • lixinyi.23@gmail.com
          #3
          Re: How do I use python object in C++

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

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

          Do I have to
          use PyModule_GetDic t() 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.

            Comment

            • Aaron \Castironpi\ Brady
              #4
              Re: How do I use python object in C++

              On Sep 23, 9:30 pm, lixinyi...@gmai l.com wrote:
              If the PyObject is a PyList, and all list items are strings,
              say a=['aaa','bbb','cc c']
              >
              How can I have a
              myArray[0] = "aaa"
              myArray[1] = "bbb"
              myArray[2] = "ccc"
              in C++?
              >
              Do I have to
              use PyModule_GetDic t() 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_FromSt ring( "aaa" ) );
              PyList_SetItem( list, 1, PyString_FromSt ring( "bbb" ) );
              PyList_SetItem( list, 2, PyString_FromSt ring( "ccc" ) );

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

              Py_DECREF( listrepr );
              Py_DECREF( list );

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

              Py_DECREF( listrepr );
              Py_DECREF( list );

              Py_Finalize();
              return 0;
              }

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

                Comment

                • Aaron \Castironpi\ Brady
                  #5
                  Re: How do I use python object in C++

                  On Sep 23, 11:06 pm, "Aaron \"Castironpi \" Brady"
                  <castiro...@gma il.comwrote:
                  On Sep 23, 9:30 pm, lixinyi...@gmai l.com wrote:
                  >
                  >
                  >
                  If the PyObject is a PyList, and all list items are strings,
                  say a=['aaa','bbb','cc c']
                  >
                  How can I have a
                  myArray[0] = "aaa"
                  myArray[1] = "bbb"
                  myArray[2] = "ccc"
                  in C++?
                  >
                  Do I have to
                  use PyModule_GetDic t() 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_FromSt ring( "aaa" ) );
                      PyList_SetItem( list, 1, PyString_FromSt ring( "bbb" ) );
                      PyList_SetItem( list, 2, PyString_FromSt ring( "ccc" ) );
                  >
                      listrepr= PyObject_Repr( list );
                      printf( "%s\n", PyString_AsStri ng( listrepr ) );
                  >
                      Py_DECREF( listrepr );
                      Py_DECREF( list );
                  >
                      /* second */
                      list= Py_BuildValue( "[sss]", "aaa", "bbb", "ccc" );
                      listrepr= PyObject_Repr( list );
                      printf( "%s\n", PyString_AsStri ng( 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_FromSt ring( "myarray" );
                  list= PyDict_GetItem( dict, name );
                  listrepr= PyObject_Repr( list );
                  printf( "%s\n", PyString_AsStri ng( 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.

                    Comment

                    • lixinyi.23@gmail.com
                      #6
                      Re: How do I use python object in C++

                      On 9$B7n(B24$BF |(B, $B8a8e(B1:15, "Aaron \"Castironpi \" Brady" <castiro...@gma il.com>
                      wrote:
                      On Sep 23, 11:06 pm, "Aaron \"Castironpi \" Brady"
                      >
                      >
                      >
                      <castiro...@gma il.comwrote:
                      On Sep 23, 9:30 pm, lixinyi...@gmai l.com wrote:
                      >
                      If the PyObject is a PyList, and all list items are strings,
                      say a=['aaa','bbb','cc c']
                      >
                      How can I have a
                      myArray[0] = "aaa"
                      myArray[1] = "bbb"
                      myArray[2] = "ccc"
                      in C++?
                      >
                      Do I have to
                      use PyModule_GetDic t() 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_FromSt ring( "aaa" ) );
                      PyList_SetItem( list, 1, PyString_FromSt ring( "bbb" ) );
                      PyList_SetItem( list, 2, PyString_FromSt ring( "ccc" ) );
                      >
                      listrepr= PyObject_Repr( list );
                      printf( "%s\n", PyString_AsStri ng( listrepr ) );
                      >
                      Py_DECREF( listrepr );
                      Py_DECREF( list );
                      >
                      /* second */
                      list= Py_BuildValue( "[sss]", "aaa", "bbb", "ccc" );
                      listrepr= PyObject_Repr( list );
                      printf( "%s\n", PyString_AsStri ng( 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_FromSt ring( "myarray" );
                      list= PyDict_GetItem( dict, name );
                      listrepr= PyObject_Repr( list );
                      printf( "%s\n", PyString_AsStri ng( 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_AddMod ule("__main__") ;
                      global_dict = PyModule_GetDic t(main_module);
                      pyObject = PyDict_GetItem( global_dict,key );


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

                        Comment

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