cppyy.gbl.RooFormulaVar object at ** does not have attribute formula

[pkalbhor]

Following simple syntax not working for latest pyROOT

lxplus$ python3
Python 3.6.8 (default, Apr  2 2020, 13:34:55) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ROOT

>>> x=ROOT.RooRealVar("x", "x", -10, 10)

RooFit v3.60 -- Developed by Wouter Verkerke and David Kirkby 
                Copyright (C) 2000-2013 NIKHEF, University of California & Stanford University
                All rights reserved, please read http://roofit.sourceforge.net/license.txt

>>> y=ROOT.RooRealVar("y", "y", -10, 10)
>>> roofor=ROOT.RooFormulaVar("gen", "x*y", ROOT.RooArgList(x,y))
>>> roofor.formula()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'RooFormulaVar' object has no attribute 'formula'

---

Version: root 6.22.02
Platform: lxplus cern

[StephanH]

Hi @pkalbhor,

the function’s visibility was changed to private when RooFormula was updated from a ROOT5 formula to a ROOT6 formula.
I guess that can be reverted, but give me a bit of time to check if it’s safe.

One question:
Do you want to change the formula or just read access? I.e., a const & or just a reference to it?

[pkalbhor]

Hi @StephanH
I just want to read the expression of the formula and save it into the string. Like this:

RooFormulaVar roofor
roofor.formula().GetExpFormula().Data()

So yes just read access is fine.
with python2 and ROOT6.18, it used to work just fine.

[StephanH]

Here’s what’s happening:

[RF] Re-expose RooFormulaVar::formula().

[StephanH]

It’s merged. Tomorrow, you can test with one of root’s nightly versions.

[pkalbhor]

Thank a lot @StephanH,
I was trying nightly version built on Thursday and for gcc-9.2.0, as below,

source /cvmfs/sft.cern.ch/lcg/nightlies/dev3/Thu/lcgenv/*/x86_64-centos7-gcc9-opt/lcgenv-env.sh
source /cvmfs/sft.cern.ch/lcg/nightlies/dev3/Thu/ROOT/HEAD/x86_64-centos7-gcc9-opt/bin/thisroot.sh

But on lxplus by default gcc-4.8.5 is used and nightly version is not available for this compiler. I tried setting alias for gcc/g++ 9.2.0 as

alias gcc='/cvmfs/sft.cern.ch/lcg/releases/gcc/9.2.0/x86_64-centos7/bin/gcc'
alias g++='/cvmfs/sft.cern.ch/lcg/releases/gcc/9.2.0/x86_64-centos7/bin/g++'

But it doesn’t work, while doing import ROOT in python3, it gives *** Break *** segmentation violation error.
Could give some details on how to correctly use nightly version of ROOT in lxplus?

[StephanH]

Somebody updated the nightlies page, and left out the information that you need dev3python3 for python3.
This worked for me:

$ source /cvmfs/sft.cern.ch/lcg/views/dev3python3/latest/x86_64-centos7-gcc8-opt/setup.sh 
$ python3 -c "import ROOT; x = ROOT.RooRealVar('x', 'x', 0); x.Print()"

RooFit v3.60 -- Developed by Wouter Verkerke and David Kirkby 
                Copyright (C) 2000-2013 NIKHEF, University of California & Stanford University
                All rights reserved, please read http://roofit.sourceforge.net/license.txt

RooRealVar::x = 0 C  L(-INF - +INF) 

(The nightlies page will soon mention an easier way to get ROOT and correct compiler in one go.)