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PythonManager.h

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//
// Smart reference + singleton to handle Python interpreter
//
//
// Original Author:  Chris D Jones & Benedikt Hegner
//         Created:  Sun Jul 22 11:03:53 CEST 2006
//

#ifndef FWCore_Python_PythonManager_h
#define FWCore_Python_PythonManager_h

#include "FWCore/ParameterSet/interface/BoostPython.h"
#include "FWCore/Utilities/interface/Exception.h"

extern "C" {
   //this is the entry point into the libFWCorePython python module
   void initlibFWCorePython();
   //void initROOT();
}

namespace {
    void
    pythonToCppException(const std::string& iType)
    {
       using namespace boost::python;
       PyObject *exc, *val, *trace;
       PyErr_Fetch(&exc,&val,&trace);
       handle<> hExc(allow_null(exc));
       if(hExc) {
          object oExc(hExc);
       }
       handle<> hVal(allow_null(val));
       handle<> hTrace(allow_null(trace));
       if(hTrace) {
          object oTrace(hTrace);
       }

       if(hVal) {
          object oVal(hVal);
          handle<> hStringVal(PyObject_Str(oVal.ptr()));
          object stringVal( hStringVal );

          //PyErr_Print();
          throw cms::Exception(iType) <<"python encountered the error: "<< PyString_AsString(stringVal.ptr())<<"\n";
       } else {
          throw cms::Exception(iType)<<" unknown python problem occurred.\n";
       }
    }

    class PythonManagerHandle;
        
    class PythonManager {
      public:
            friend class PythonManagerHandle;
            static PythonManagerHandle handle();

      private:
             PythonManager();
             ~PythonManager() { Py_Finalize(); }
             void increment() { ++refCount_; }
         void decrement() { --refCount_; if(0==refCount_) delete this; }
             unsigned long refCount_;
             std::string initCommand_;
    };

    class PythonManagerHandle {
      public:
            ~PythonManagerHandle() { manager_.decrement(); }

            PythonManagerHandle(PythonManager& iM):
              manager_(iM) {
              manager_.increment();
            }

            PythonManagerHandle(const PythonManagerHandle& iRHS) :
              manager_(iRHS.manager_) {
              manager_.increment();
            }
                
      private:
            const PythonManagerHandle& operator=(const PythonManagerHandle&);
            PythonManager& manager_;
    };

    PythonManagerHandle PythonManager::handle() {
        static PythonManager* s_manager( new PythonManager() );
        return PythonManagerHandle( *s_manager);
    }

    PythonManager::PythonManager() :
        refCount_(0),
        initCommand_(
            "import sys\n"
            "sys.path.append('./')\n"
            "import ROOT\n"
            "ROOT.gSystem.Load(\"libFWCoreFWLite\")\n"
            "ROOT.AutoLibraryLoader.enable()\n"
            "import libFWCorePython as edm\n")
    {
       Py_InitializeEx(0);
       using namespace boost::python;

       if(PyImport_AppendInittab("libFWCorePython",initlibFWCorePython)==-1) {
         throw cms::Exception("InitializationFailure" )
          <<"failed to add libFWCorePython python module to python interpreter";
       }
       object main_module((
                           boost::python::handle<PyObject>(borrowed(PyImport_AddModule("__main__")))));
       object main_namespace = main_module.attr("__dict__");
       try {
           object result((boost::python::handle<>(PyRun_String(initCommand_.c_str(),
                                           Py_file_input,
                                           main_namespace.ptr(),
                                           main_namespace.ptr()))));

       } catch(...  ) {
         throw cms::Exception("Configuration") << "test";
       }

    }
}

#endif // FWCore_Python_PythonManager_h

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