Reading HepMC weights with python

[Ameen]

Dear ROOT experts,

Using a C++ macro, I usually read the weights of events using:

ExRootTreeReader *treeReader = new ExRootTreeReader(&chain);
Long64_t numberOfEntries = treeReader->GetEntries();
TClonesArray *branchEvent = treeReader->UseBranch("Event");
for(Int_t entry = 0; entry < numberOfEntries; ++entry)
     {
        treeReader->ReadEntry(entry);
        HepMCEvent *event = (HepMCEvent*) branchEvent->At(0);
       cout << event->Weight << endl;
     }

What is the pythonic way of doing this?

Thank you,
Amin

[etejedor]

Dear Ameen,

There is a more Pythonic way to iterate over the entries of a TTree in Python and accessing its branches, as illustrated in this example.

However, in your C++ macro you are using a wrapper class for TTreeReader (ExRootTreeReader), so you can’t use the pythonization directly. You can still write a range loop in Python to iterate over the entries, but the rest of the code should look very similar to the C++ version.

Best,
Enric

[Ameen]

Dear Enric,

Thank you for the reply. I will implement the method used in the example.

Best,
Amin

[etejedor]

Dear Ameen,

Sure, let us know if you need any other help.

Best,
Enric