TChain* openChain(TString runs, TString path,TString pattern)
{
  TString basedir = gSystem->Getenv("VMCWORKDIR");
  TChain* chain=new TChain("cbmsim");
  TString pythonScript=basedir+"/macro/tpc/FOPI/parseFiles.py";
  TPython::LoadMacro(pythonScript);
  PyFileParser fp;
  fp.setPath(path.Data());
  fp.setRuns(runs.Data());
  fp.setPattern(pattern.Data());
  fp.setInRunFolder();

  fp.makeFileList();
  int nFiles = (int)fp.getNum();
  std::cout<<"found "<<nFiles<<" files\n";
  for(int i=0; i<nFiles; i++) {
    chain->AddFile((char*)fp.getFile(i));
    std::cout<<"Add file "<<(char*)fp.getFile(i)<<" to reco chain"<<std::endl;
  }
  return chain;
}