SetDirectory(0) using PyROOT inside a function

[fsili]

Dear experts,

I have a doubt on how SetDirectory works when using it inside a Python function.

I have a .root file which contains severals historams, in this case I am using a simple one for the sake of simplicity. I want to retrieve this histogram from the file, but this process is being done inside a function GetHist.

First, I tried this:

from ROOT import *

def GetHist():
    file = TFile("data_MC_original.root", "READ")
    h1 = file.Get("h_ptbin3_etabin6_nom_OrigDT")
    h1.SetDirectory(0)
    file.Close()
    return h1

h = GetHist()
c1 = TCanvas("", "", 800, 600)
h.Draw("hist")
c1.Update()

In the above case everything goes right. However, when I try changing the function to this

def GetHist():
    file = TFile("data_MC_original.root", "READ")
    h1 = file.Get("h_ptbin3_etabin6_nom_OrigDT")
    h1.SetDirectory(0)
    h_copy = h1.Clone()
    file.Close()
    return h_copy

I get an error saying

'CPyCppyy_NoneType' object has no attribute 'Draw'

So what’s happening there?

Other thing I tried was cloning the histogram ‘by hand’

from ROOT import *

def GetHist():
    file = TFile("data_MC_original.root", "READ")
    h1 = file.Get("h_ptbin3_etabin6_nom_OrigDT")
#    h1.SetDirectory(0) # With or without this, same error
    nbins = h1.GetNbinsX()
    xlow = h1.GetXaxis().GetXmin()
    xup = h1.GetXaxis().GetXmax()

    h_copy = TH1F("", "", nbins, xlow, xup)

    for bin in range(1, nbins):
        content = h1.GetBinContent(bin)
        h_copy.SetBinContent(bin, content)
    file.Close()
    del h1
    return h_copy

In that case, I get the same error as before:

'CPyCppyy_NoneType' object has no attribute 'Draw'

That last case worries me most. I have a histogram created by hand, not related at all (only the content, which is set by hand as well) with the file, so why this keeps happening?

EDIT: Also, sometimes when I run this version which works

def GetHist():
    file = TFile("data_MC_original.root", "READ")
    h1 = file.Get("h_ptbin3_etabin6_nom_OrigDT")
    h1.SetDirectory(0)
    file.Close()

    nbins = h1.GetNbinsX()
    xlow = h1.GetXaxis().GetXmin()
    xup = h1.GetXaxis().GetXmax()

    h_copy = TH1F("", "", nbins, xlow, xup)
    for bin in range(1, nbins):
        content = h1.GetBinContent(bin)
        h_copy.SetBinContent(bin, content)

    del h1
    return h_copy

the process “python 3.7” keeps running in my computer and using 100% of CPU. I have to manually kill it in Activity Monitor (using MacOS Catalina). Why this is happening?

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Any help is very much appreciated!

Thank you very much!

Cheers,
Francisco

[etejedor]

Hi,

About the first case, it looks like when you do the Clone, the cloned histogram is tied to the file, so when you close the file, the C++ histogram underneath is deleted and its Python proxy becomes None. Can you try to do h_copy.SetDirectory(0)? That should work and you won’t need to do the copy by hand.