Using PyROOT with PROOF

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Using PyROOT in PROOF

Preparation

Write one main algorithm in python and one wrapper in C++. eg.,

$ cat PyTest.py

import ROOT
class PyTest(ROOT.TSelector):
    def __init__(self):
        ROOT.TSelector.__init__(self)
        self.fChain = None

    def Init(self,tree):
        print "in Init"
        self.fChain = tree

    def Process(self,entry):
        print "in Process"
        self.fChain.GetTree().GetEntry(entry)
        print self.fChain.EventNumber

==============================================

$ cat Wrapper.h

#ifndef Wrapper_h
#define Wrapper_h

#ifndef __CINT__

#if defined(linux)
#include <stdio.h>
#ifdef _POSIX_C_SOURCE
#undef _POSIX_C_SOURCE
#endif
#ifdef _FILE_OFFSET_BITS
#undef _FILE_OFFSET_BITS
#endif
#endif // defined(linux)
#include "Python.h"
#else  // __CINT__
struct _object;
typedef _object PyObject;
#endif // !__CINT__

#include "TSelector.h"

class Wrapper : public TSelector
{
public :
   Wrapper(TTree * /*tree*/ =0) : m_self(NULL) { }
   virtual ~Wrapper() { }
   virtual Int_t   Version() const { return 2; }
   virtual void    Init(TTree *tree);
   virtual Bool_t  Process(Long64_t entry);

private:
   PyObject* m_self;
};

#endif 

==============================================

$ cat Wrapper.C

#include "Wrapper.h"
#include "TPython.h"

#define MY_SELECTOR "PyTest"

void Wrapper::Init(TTree *tree)
{
  if (!tree) return;

  // just to initialize Python/TPython stuff
  TPython::Exec("import ROOT");

  if (m_self == NULL)
    {
      PyObject* module = PyImport_ImportModule(MY_SELECTOR);
      if (module != NULL)
        {
          PyObject* pclass = PyObject_GetAttrString(module,MY_SELECTOR);
          if (pclass != NULL)
            {
              PyObject * args = PyTuple_New(0);
              m_self = PyObject_Call(pclass,args,NULL);
              Py_DECREF(args);
              if (m_self != NULL)
                {
                  /*
                  TClass* klass = tree->IsA();
                  PyObject* ptree = PyROOT::BindRootObject((void*)tree,klass );
                  */
                  char * ptree_name = "_py_tree";
                  TPython::Bind((TObject *)tree, ptree_name);
                  PyObject* pmain = PyImport_AddModule("__main__");
                  PyObject* ptree = PyObject_GetAttrString(pmain, ptree_name);
                  PyObject* result = PyObject_CallMethod(m_self, "Init", "O", ptree);
                  if (result != NULL)
                    Py_DECREF(result);
                  else
                    PyErr_Print();
                  Py_DECREF(ptree);
                }
              else
                  PyErr_Print();
              Py_DECREF(pclass);
            }
          else
              PyErr_Print();
          Py_DECREF(module);
        }
      else
          PyErr_Print();
    }
}

Bool_t Wrapper::Process(Long64_t entry)
{
  if (m_self == NULL) return kFALSE;

  PyObject* result = PyObject_CallMethod( m_self, "Process", "L", entry );
  Py_DECREF(result);
  return kTRUE;
}

==============================================

You may add more methods like SlaveBegin() and may replace PyTest with your algorithm name.

Run

$ root.exe

// open session
TProof::Open("acas0420.usatlas.bnl.gov");

// add Python to LD_LIBRARY_PATH 
gProof->AddDynamicPath("/afs/usatlas.bnl.gov/cernsw/lcg/external/Python/2.4.2/slc4_ia32_gcc34/lib")

// need this one because libpython2.4.so is not loaded automatically
gProof->Exec("gSystem->Load(\"libpython2.4.so\")")

// add Python to include path
gProof->AddIncludePath("/afs/usatlas.bnl.gov/cernsw/lcg/external/Python/2.4.2/slc4_ia32_gcc34/include/python2.4")

// set PYTHONPATH
gProof->Exec("gSystem->Setenv(\"PYTHONPATH\",\"/usatlas/u/maeno/proof:/afs/usatlas.bnl.gov/cernsw/lcg/external/root/5.14.00/slc4_ia32_gcc34/root/lib\");")  

Replace /usatlas/u/maeno/proof with the directory where your python algorithm exists.

  
// create dataset
TDSet *d = new TDSet("TTree","CollectionTree")
d->Add("root://acas0420.usatlas.bnl.gov//data/cache/HPTV/user.TARRADEFabien.trig1_misal1_csc11.005013.J4_pythia_jetjet.Athena_12.0.6.GroupArea_12.0.6.6.Jamboree_II-HightPtView-00-00-30.AAN.AANT0._00065.root");      

# execute the Python algorithm via the wrapper
d->Process("Wrapper.C+")

Caveat

• The following doesn't work with v.5.14.00g/v5.16.00 because TSelector::GetSelector("PyTest") returns NULL due to G__ClassInfo("PyTest").IsBase("TSelector")==0 and G__ClassInfo("PyTest").New()==NULL

        $ root.exe
        root [0] TPython::LoadMacro("PyTest.py")     
        root [1] ....
        root [N] TDSet *d = ...
        root [M] d->Process("PyTest")

• PyTest.py would be uploaded to the cluster using TProof::Load() with v5.16.00
• LD_LIBRARY_PATH and PYTHONPATH could be set on the server side

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Major updates:
-- TWikiAdminGroup - 09 Feb 2012