Reading branches from a TTree with PYROOT

[mendoza]

Dear experts,

I am having trouble to read info from the branches of a TTree using the following code:

    z = array('d',[0.])
    tree.SetBranchAddress("L0_END_VZ",z)
    pt = array('d',[0.])
    tree.SetBranchAddress("L0_PT",pt)

    for j in range(tree.GetEntries()):
        tree.GetEntry(j)
        print(z[0])
        print(pt[0])

   and I got in the prints very small numbers like 5.721481036e-315 I don't understand because this method used to work for me...

Thanks in advance for your time!

Diego

[Wile_E_Coyote]

tree.Print()

[mendoza]

yeah they were float numbers instead of doubles… dumb error, thanks!
Also, there is another branch I want to store:

proton_HASVELO : proton_HASVELO/O

they are doubles, can I use for example:
ar = array(‘i’,[0]) to store them?

[mendoza]

sorry they are “booleans”, I meant

[Wile_E_Coyote]

Well, "/O" means ROOT “Bool_t” which is then probably an ordinary C++ “bool”.
I think “numpy.array” supports “dtype=bool”.

[mendoza]

Perfect, works for me. Thanks!

[eguiraud]

Hi @mendoza ,

please note that while reading TTree data from a Python for loop works fine in general, it is also much slower than alternative interfaces (namely RDataFrame) so make sure you don’t use raw Python loops for large-scale, full-blown analysis.

Cheers,
Enrico