TGraph visualization through PyROOT

Hi I have written a script in PyROOT through my python interpreter (PyCharm) which takes data from a TTree and creates a TGraph. The script runs smoothly however I no visualization of the graph appears, does anyone else have this issue? I have tried with another script found on the ROOT guides as well which results in the same issue. The script I found and have used for an example to get a better understanding og TGraphs through python is:

from __future__ import print_function
import ROOT
from math import sin
from array import array

c1 = ROOT.TCanvas( 'c1', 'A Simple Graph Example', 200, 10, 700, 500 )
c1.SetFillColor( 42 )
n = 20
x, y = array( 'd' ), array( 'd' )

for i in range( n ):
    x.append( 0.1*i )
    y.append( 10*sin( x[i]+0.2 ) )
    print(' i %i %f %f ' % (i,x[i],y[i]))
gr = ROOT.TGraph( n, x, y )
gr.SetLineColor( 2 )
gr.SetLineWidth( 4 )
gr.SetMarkerColor( 4 )
gr.SetMarkerStyle( 21 )
gr.SetTitle( 'a simple graph' )
gr.GetXaxis().SetTitle( 'X title' )
gr.GetYaxis().SetTitle( 'Y title' )
gr.Draw( 'ACP' )
# TCanvas.Update() draws the frame, after which one can change it
c1.GetFrame().SetFillColor( 21 )
c1.GetFrame().SetBorderSize( 12 )

Does anyone know why I don’t get a visualization of my graph when running this code?

Thank you for all help!

Do you see the canvas ? an empty canvas ?
as far as I can see what you are doing seems fine.
@etejedor may know .


Can you run your script with python -i ?

It might be that the Python interpreter process is finishing and your canvas goes away with it. The -i option keeps the Python process alive.

1 Like

Thank you for response. When I try to run the script this way I receive this response:

Traceback (most recent call last):
File “”, line 2, in
import ROOT
File “/Applications/root/lib/”, line 24, in
import cppyy
File “/Applications/root/lib/”, line 61, in
import libPyROOT as _backend
ImportError: dynamic module does not define module export function (PyInit_libPyROOT)

It may be worth mentioning that I am currently working on a project in physics and when my first issues with running PyROOT scripts arose my supervisor adviced me to run the script by:

which -a python2.7

This method runs the script successfully however no canvas opens and no visualization appears. The only result I get from this is all the points corresponding to each i in the for loop printed onto the terminal.

No, nothing appears except for all the coordinate points printed onto the terminal.

Note your macro is very simple and can be easily converted in C++. It is very similar to the first example given in the TGraph reference guide. Unless you are obliged to use python that might be a solution (as your python installation does not seem to be optimal).

The reason of this error is that you are using a ROOT installation that was compiled for Python3, but to run your script you are using Python2. Please try running your script with Python3.