Hist Draw() from TTree, canvas not updating in ipython (ok in python)

ROOT
#1

I have a .root file containing a tree with branch of histograms.
In ipython, I can load the file and Draw the histogram. But when I try to Draw the next histogram, the canvas does not update. The same code, run from a standard python prompt, works fine…

In [] import ROOT
In [] f=ROOT.TFile("test.root")
In [] t=f.Get('raw')
In [] t.Print()
******************************************************************************
*Tree    :raw       : title of tree                                          *
*Entries :        3 : Total =          242676 bytes  File  Size =      36090 *
*        :          : Tree compression factor =   6.78                       *
******************************************************************************
*Br    0 :wf        : TH1I                                                   *
*Entries :        3 : Total  Size=     242284 bytes  File Size  =      35676 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   6.78     *
*............................................................................*
In [] t.GetEvent(0)
In [] t.wf.Draw() # canvas is created and TH1I is drawn
In [] t.GetEvent(1)
In [] t.wf.Draw()  # canvas does not update...

Are there any known issues along these lines with ipython?

$ root-config --version
6.08/02
$ python --version
Python 2.7.5
$ ipython --version
5.1.0
#2

There was a issue supporting iPython 5 (see sft.its.cern.ch/jira/browse/ROOT-8288), but the fix is already in 6.08/02. So, it much be something different. I’ll try to reproduce. Can you put the file with the histograms in a public accessible place?
Pere

#3

Sure, here’s the file.
test.root (41.7 KB)

#4

Sorry for the delay. I can reproduce and I need to investigate further.
Workaround is to explicitly call Update() to the TCanvas.

In [3]: c = ROOT.TCanvas()
In [4]: for e in t:
    ...:     e.wf.Draw()
    ...:     c.Update()
    ...:     time.sleep(1)
    ...:

Cheers, Pere

#5

ok, thanks for the workaround. Looking forward to what you find.