Reading TChain events

ROOT
1

What is a trick in TChain events reading? I have a very simple script (in the attachment) which works fine with TTree, but not with TChain! Please help!!

Thanks a lot in advance,
Alexander Zvyagin.
b.py (977 Bytes)

2

Hi Alexander,

please use ROOT.AddressOf() when passing the event object to SetBranchAddress:tree.SetBranchAddress( 'Event', ROOT.AddressOf( event_ID ) )
The interface specifies ‘void*’, so that is what ends up in the dictionary. However, it really needs ‘void**’. There’s an automatic correction for TTree::SetBranchAddress() on the python side, which does unfortunately not propagate because TChain::SetBranchAddress() is overriding it.

You should also be able to access the event object directly:print tree.Event.run, which will work for both TTree and TChain.
HTH,
Wim

3

Hi,

that worked, thanks!

    tree.SetBranchAddress( 'Event', ROOT.AddressOf(event_ID) )

I tried myself this only this one (which did not work):

    tree.SetBranchAddress( 'Event', ROOT.AddressOf(event_ID,'run') )

The line

print tree.Event.run

(which I also tried to use) prints me None.

Thanks again, I am happy with the solution with ROOT.AddressOf()
Alexander.