How to get NbinsX with pyroot?

ROOT
1

Hi, I want to get NbinsX in python , the code is

import ROOT
from ROOT import gRandom, TH1, TH1D, TH2D, TCanvas
fdata=ROOT.TFile.Open(“data.root”)
fbkg = ROOT.TFile.Open(“bkg.root”)

hdata = fdata.Get(“z_pt”)
hbkg = fbkg.Get(“z_pt”)

h1=hdata
for i in range(1,len(hdata.GetNbinsX())+1):
content = hdata.GetBinContent(i)-hbkg.GetBinContent(i)
h1.SetBinContent(i,content)

c1 = ROOT.TCanvas(“c1”, “c1”,5,50,500,500)
c1.SetLogy()
h1.Draw("")
c1.SaveAs(“zpt.png”)

but there is an error:
Traceback (most recent call last):
File “r1.py”, line 16, in
for i in range(1,len(hdata.GetNbinsX())+1):
AttributeError: ‘TObject’ object has no attribute ‘GetNbinsX’

Do you have some suggestion?

2

Hi @Jen,

It sems that the type that you are expecting from fdata.Get("z_pt") is a THn class, but you are getting a plain TObject. I will invite @etejedor to this thread; he will be able to shed some light on this.

Cheers,
J.

3

Hi,

I don’t think casting TObject to a THn is necessary in PyROOT. Try changing

for i in range(1,len(hdata.GetNbinsX())+1):

to

for i in range(1, hdata.GetNbinsX()+1):

instead.

4

Just a guess, but in principle in Root you can use (in C macros) Get<Class>('key')
If you know in advance the type of the object you take, you can try with

hdata = f.Get["TH1D"]("z_pt")
5

Hello,

The reason might be that z_pt can’t be retrieved from data.root, so what you get back is an (empty) TObject.

Can you do:

hdata = fdata.Get(“z_pt”)
print(hdata)

What does it print?

Another thing you can try is:

hdata = fdata.z_pt

Does it throw an attribute error?

6

Hi,
I found that ‘z_pt’ can’t be retrieved from ‘data.root’, because there is some problem with the root file.
Thanks for your solution.
And thanks for all of you!
Cheers